MIDI Thru Latency Issue

Now that Pro Tools is finally 64-bit, I am considering switching over from Cubase in order to more easily collaborate with some fellow songwriters. However, I am experiencing a "deal breaker" MIDI latency issue with the PT v11.1.2 demo running under Windows 7 Pro 64-bit.



Firstly, I should probably mention that there is no appreciable latency when playing (via my Virus keyboard) virtual instruments in Pro Tools. My RME RayDAT audio buffer is set 128 samples and performs well.



However, when playing any of my hardware synths (that are monitored in Pro Tools via Aux Inputs,) there is a very noticeable lag. I am pretty sure the issue is related to the MIDI thru function in Pro Tools because if I play my Virus Kb, for instance, directly into Pro Tools (by disconnecting its MIDI cable and turning on the keyboard via the "Local On" parameter,) there is no latency. It's only when I use the MIDI thru in Pro Tools that I experience the significant lag.



My hardware synths are connected to my PC via three MOTU MIDI Express 128 interfaces. I don't experience this MIDI thru latency issue in Cubase when using the MOTU interfaces.



I have disabled the MIDI Delay Compensation preference in Pro Tools. But this didn't eliminate the lag.



I would be extremely grateful for any suggestions on how to resolve this issue. As it stands, there is no way I could use Pro Tools with this MIDI thru latency problem. I would just stick with Cubase (which works great) and export my tracks as audio files if I need to collaborate with someone who is using Pro Tools.



Thanks for your help!