... or actually : For Engine#1 and Engine#2, those being the only ones running on XP.
But people ... since I had to listen to this a bit for testing purposes ... get Vista if you love good sound ...
Okay. Gapless should not be worse that it was for #1 and #2 with WAVs.
SQ for FLAC cannot be different than for original WAV files.
When a FLAC is playing, a FLAC icon will show now. Just to inform you.
Additionally, when Engine#1 can't cope with the file size (64MB, or actually, the limit was put to 6 minutes), XXHighEnd will auto-switch to Engine#2 (and back to #1 after the track concerned).
When this happens, your selected Engine#1 will show in red (see below screen shot).
Although it was not reported, when Engine#3 (thus Vista) had played, switching to Engine#1 and pressing Play caused an error. This is (at changing the Engine from #3 to #1) replaced now with a message that the player has to be restarted. Please note if this is not done, pressing Play anyway will cause nothing to happen further.
Edit : Hmm ... I deleted a comment about the expected SQ by accident as it seems. By now I can tell : even more aggressive than 0.9p / 0.9q. So no good for that (Vista/Engine#3).