well, most of them are for 'internal use only' -- keep them as-is
"pan/balance" is for wave playback (whether the 'pan' control is stereo-like or mono-like) -- the default is 'pan'
(in pre-3534 versions it was 'balance')
"interpolated src" -- for CL compatibility (if you like the way CL plays back the audio) -- CL's method is a little bit worse

"multichannel volume" -- if you experience problems with multichannel volume, turn it on
"don't smooth" -- if you hear clicks (or experience any other audio artifacts) when changing volume/pan -- turn it on
as for 'synth': it is much more complex -- if you need realtime resonance, turn it on
bank selection method: if you midi application doesn't allow you to change that, set it here
-- the rest are for compatibility only
/E