Sure:-

Main machine - ASUS P9X79, i7 6core 3.4 GHz, 64GB RAM, Echo Layla 3g soundcard, System on 240GB SSD, Vienna samples spread over 3x480GB SSD

1st Slave - Gigabyte GA-X58A-UD3R, i7 4core 3.2 GHz, 24GB RAM, System on 240GB SSD, Vienna Samples on 240GB SSD, other samples on 2x1.5TB Western Digital 7200rpm HDD

2nd Slave - ASUS P8Z77-VLX, i7 4core 3.2GHz, 16GB RAM, System on 1TB HDD, Vienna samples on 240GB SSD

All three machines are connected to a Belkin f5d5141-5 switch via cat 6 cables. I've set them all with jumbo frames enabled, green LAN disabled, and static i.p addresses.

First the obvious points :

Any Virus Scanner ?

Have you tried to throw away iTunes  with all the Apple stuff ( Apple Mobile whatever... ET wants to phone home...)

To be honest, I don´t think that is is something like that.

What about IRQ settings, memory or other ressource sharing of the Lan onbord chipset or the audio interface with other units ?

Any Firewire devices, Liquidmix, UAD, SSL Duende, TC Powercore etc ?

Your drive specs are crazy, I wouldn´t expect any problem with that unless driven horribly hard.

Is the Echo Layla  working stable without Vienna or do the problems only occur when both are at work ?

Hi

Your configuration is impressive !

Did you check the load of each computers ? OK ? 

Why did you spread your Vienna samples on the three computers ?

What VSL  lib do you have to use almost 2 TB 

Are your SSD in a Raid 0 ?

What other player do you use ?

Do you use MIR PRO ?

Are your SSD on SATA III ?

I would run speed test on the slaves to see if there is not one that is behind.

Did you check the speed of the SSD on your different boards ? (some people had very bad surprise on loosy moterboards running there ssd at 1/2 the speed) 

If you work with the main and one slave are your problems gone ? (if yes you may have to put 2 x ethernet cards in the main and plug directly the slave on separate ports and not use your gigabyte switch

It is said that it is better to have the same slaves when you work with video, with audio it could be the same ! 

When you say "static" IP adresses, do you mean FIX  IP adresses ?

The joke of the day : go on a 12 core Macpro ! LOL

Not sure, but i would ask myself how many audiochannels i was sending over the network from both slaves? Also at what sample and bit rates.

Do you run other network demanding software such as remote desktop? 

Would a qos router or switch make a difference in order to prioritize net traffic?

Are the dropouts occurring in the network ? or could it be one of the machines itself? 

Hi again Cyril, and thanks for taking the time

@Another User said:

Are your SSD on SATA III ?

I would run speed test on the slaves to see if there is not one that is behind.

Did you check the speed of the SSD on your different boards ? (some people had very bad surprise on loosy moterboards running there ssd at 1/2 the speed) 

If you work with the main and one slave are your problems gone ? (if yes you may have to put 2 x ethernet cards in the main and plug directly the slave on separate ports and not use your gigabyte switch

I'm fairly sure all the drives are on SATA III - I checked the manuals to the motherboards. They're set to IDE rather than AHCI, but I believe Intel processors don't support AHCI anyway.

I'm not sure how to run speed tests. I ran the system rating thing in Windows, which returned a 7.9 out of 7.9 for data transfer speeds on each machine. Also not sure how to check the speed of the SSDs.

Sadly the problems don't go away when I just connect up two machines directly. I did that when setting up the first two, and things seemed to get better for a while - to the point where I was about to buy a new switch - but then the problems came right back, and only went away (or at least got a lot better) when I turned on jumbo frames.

And yes I do mean fixed IP addresses.

@MWE said:

Not sure, but i would ask myself how many audiochannels i was sending over the network from both slaves? Also at what sample and bit rates.

Do you run other network demanding software such as remote desktop? 

Would a qos router or switch make a difference in order to prioritize net traffic?

Are the dropouts occurring in the network ? or could it be one of the machines itself? 

Hi MWE,

I'm not sure about the number of audio streams. As I understood it the summing of audio happens on each machine, so that all that is being passed over the network is a stereo channel, and the load remains fairly similar all the time. In any case, so far I'm only experimenting with one instrument at a time, so the load must be reasonably minimal.

The only other thing I'm aware of running on the network is Synergy, which shares the mouse and keyboard from my main machine. I guess it's possible that this is the issue. I always ran it when I was on XP without any issues, but have been out of the game for a bit, and Synergy is now completely rewritten for 64bits, so I guess it's not safe to assume that it's ok.

Not sure about the router idea - I might resort to trying it.

THe problem is definitely on the network. I have a USB audio interface which I can use to get audio out of the slaves, and playing them as standalones doesn't give any issues.

@Pingu said:

THe problem is definitely on the network. I have a USB audio interface which I can use to get audio out of the slaves, and playing them as standalones doesn't give any issues.

You need a PC specialist !

Your problem seems to be on the Windows's  side 

you can try this :

http://cyrilblanc.fr/site_principal/slave_mac.html

it's for a Master Mac and a slave Mac, but you can do this with 2 x PC

@Another User said:

The only other thing I'm aware of running on the network is Synergy

Considering what it does, not a likely cause.

Thanks guys, you're quite right, I'd completely missed that it was possible to send audio in separate channels - I assumed that VEPro just had a stereo out. On the other hand I don't think that will be the issue, as I'm only running one instrument per slave so far, and just letting it go through the main out of VEPro.

just an idea :  add a second Ethernet adaptor on your Macbook pro so you have one per slave ?

Provided that the buffer settings (both vepro & audio )are not excessive and increasing them does not make a difference, I would (given the configuration and performance so far) :

1. Verify the network cabling.

2. Verify the switch.

3. Test network card. (Including reverting to the factory driver configuration).

Btw is this all you have connected to the switch?