1) Tracked down one part of why GUS sounded bad in Star Control 2 with dosbox-X..
I was using 0.74 configs and they did not have this line:
dynamic kernel allocation=false
For anyone testing SC2, be sure to start with starcon2.exe /S:GRAVIS and check the map for coords - the map bypass hacks (incl. GOG's) appear to bring about audio bugs with gus emulation depending on what dosbox build is running it.
2) I checked the reversed stereo issue extensively (bought the first ACE rev with reverse stereo) and it appears -X branch has the GUS stereo swapped incorrectly just like the first ace card. One test is to run doom(which doesn't allow reversing stereo), idclev 1 3, and listen where the shots come from. the LFN build on other thread has this right (I believe it's based on recent SVN so that should be ok too)
This is possibly a regression of X-branch caused by the stereo width patch and misleading videos recorded with the reversed stereo in ACE rev 1.0 leading as with older build the stereo is not reversed but the width does not match the typical very wide gus sound (which you could well argue is too wide for headphones but that's how it's in the hw, so similar width adjustment in mixer as in winuae would be useful).
3) There is still some subtle glitch in all dosbox builds I tried, most noticeably in OMF menu theme beginning. It's not present on hardware. I think it can be briefly heard in other places in "quiet" songs but much more rarely.
edit: After further comparisons with ace 1.0 hw, it seems that the OMF 3) issue is the clearest one with emulation having some problem. The hw had a short glitchy sound in SC2 few times in my short test.