defenatly have to agree with ChickenMan!
TMPGenc is fairly good, but best SVCD Quality can be achived with
CCE.
But since you now have tried encoding with TMPGEnc, and still have the same problem i begin to wonder if the sound on your source file is proper in the 1st case, have you checked the source if its o.k. yet ?!?
Besides, there are a few restrictions to the SVCD Standard concerning BitRates, maybe your standalone plays SVCD but not XSVCD, so make sure to total encoded BitRate is proper!
Greetnx