I think the thing you are looking for is ReWire, the Propellerheads protocol to send audio from app to another application ( ReWire Client -> ReWire Host ). Low Latency audio in windows means exclusive audio ( 1 application at a time sending stuff to the sound card ). So you would have to see if your "Midi Studio without Support for VST mode" ( Reason?) supports ReWire. of course if all you want to do is play 2 VSTs at the same time, almost any DAW can do this, just set the midi inputs on two separate tracks to the same channel, and arm both of them for recording. Also there are plugins that host plugins ( AKAI VIP, Wusik X42 ) so you could accomplish that in that manner as well. If you update your question with some specifics I could answer much better.