I was told to "Change the 3/4 to the full ie 544" in FITCD. I don't use FITCD... so obviously, I don't know if that's the trick or not. I was able to get the templates to work on an 1100W by changing the resolution settings in TMPGEnc (the standard 352x240 for MPEG1, 480x480 for MPEG2). This method seriously reduces the quality of video. The Apex does NOT like non-standard resolutions... which is too bad.
I've given up on my Apex as far as XVCD support. My Sony player (DVP-S530) blows the Apex away on all counts, and most importantly it accepts the KVCDx3 templates as-is. Now, I just consider the Apex a backup player that I will occasionally use for Region 2 DVDs and for when I need to turn off Angle Icons for capture purposes (for some reason, you can't turn those damn things off on the Sony!)
Good luck! I'm fed up with the thing!