I have Miroslav CE but rarely use it, so Miroslav 2 might work differently now, and this is a bit tedious but it will work:
Go to the synth rack and insert it. The Insert Synth Options menu pops up. Make sure the Simple Instrument track box is NOT checked. Make sure the Midi Source, All Synth Outputs (either mono or stereo), the Synth Property Page , and Synth Rack boxes ARE checked (I'd advise checking the Synth Rack Folder box is checked when using any multitimbral instrument is checked too). Click OK.
8 audio tracks and 1 midi are created. Drag the midi track to track 1. Right click on the midi track and select clone, then enter how many Repitions (midi tracks) you want (probably 7), Starting Track 2.
Click on track the 1st midi track and load something into the 1st slot in Miroslav. The input can be Omni, the output should be Philharmonic-1. In the Inspector make sure the Channel is set to Midi Channel = 1:Philharmonic. You should hear it, or there's a different problem
Then load another sound in to the second slot Miroslav and then click on Channel 2 in Sonar, and in the Inspector change the Midi channel to Midi Channel = 2:Philharmonic. You should hear the new instrument.
I'd go ahead and repeat the routing with midi tracks 3-8 then save as a track template. It works fine here.
Good luck.