Thanks, Bapu. That's pretty interesting, and different from what I get in both X3 and Platinum. What I see in both X3 and Platinum is that the first time I start playback after enabling solo on the audio track, the MIDI meter shows activity, but there is no output from the synth. If I restart playback with the audio track solo still enabled, the MIDI meter goes quiet as well.
Both your X3 and Platinum vids are a little odd in that when you start playback with nothing soloed, the MIDI meter is showing no activity, but the audio meters are. Then when you solo an audio track, the MIDI track meter becomes active. What's up with that? Also I saw you initially reach for the folder's solo button, and it appeared you clicked it, but it did not enable...?
After seenig that, I tried putting my MIDI track in the same folder together with the Audio outputs. That appeared to work momentarily, but then broke again the next time I started playback.
I'll have to keep looking at it.