Probably not what you want to hear, but if you're wanting to use multiple instances of VI and VE to get around the RAM limits under OSX 32bit then I'd really recommend purchasing VE3 - even if you just use it on your local host. Using VE2 otherwise is hideously tricky
You need to use something like the IAC for MIDI and then route the audio from the standalone VI/VE to one of the RME outputs. The same RME output can be routed using the Fireface control panel back to a Fireface Input which can then feed an audio channel input in Logic.
Alternatively you could investigate using something like soundflower to route the audio.
Personally I'd shell out €95 on VE3 much easier, although it's a cop out to your original question
Best
Tim