If I understand correctly, Logic takes the track with the most latency in your entire mix, and then delays all the other tracks by that amount, in order to apply automatic delay compensation.  As a result, if you have any plugins in your mix which introduce latency, everything else will be delayed as a result.  Not an issue with normal audio and MIDI tracks (Logic probably bypasses ADC when the transport is static anyway), but for your audio input tracks, Logic is having to delay them all the time at the mix's maximum latency, because they are 'live' all the time.

I can't believe I just explained that so badly!!

My suspicion is that your Powercore Reverb will introduce a LOT of latency.  Most DSP based effects introduce even more latency than native effects, because the audio has to be routed to the device in question via the PCI or Firewire bus, and then back into 'native' land.  I use a Powercore Firewire and also use UAD-1 cards - tha latter introduce huge amounts of latency - depending on the host often twice the host buffer setting or more.

The best way to test whether it's ADC causing the latency problem is just to disable it in Logic (in Audio Settings or Audio Hardware Settings from memory), and see if the latency improves.  If it doesn't then the issue must be elsewhere, and given that VE is so responsive when routed direct to hardware, that suggests the issue must be with Jack OSX.

I route my entire Logic mixes into ProTools HD on a different system, via 64 channels of lightpipe, and then mix in ProTools in real-time (ie. with the arrangement still running in Logic).  I just happen to like the ProTools mixer, have lots of plugins on that machine and have just always worked that way.

All the best

Jules