Bob I have found your observations about the new PS3 sound sets to be true on the PS3 engines I formerly owned or have heard at the dealers. For me, I like lots of volume, and would rather have to dial it down if its too loud.
I was quite excited about the most recent MTH GS4 Daylight offering, but was quickly disappointed after hearing it; enough so that I passed on the purchase. I have both the PS2 GS2 and the PS2 GS4 and sound volume and robustness is not even a fair comparison to the PS3. Also the PS2 GS4 when I first purchased was also very weak in the sound volume dept. but I was sent a new sound file from MTH and it made a day and night difference.
I tried some aftermarket speakers described as "FatBoy" equivalent, but they turned out to be worse than the MTH originals.
I also just recently tried to incorporate a micro-amp into the sound system hoping to achieve increased volume, but so far I have been unsuccessful. I am getting higher volume, but I'm also getting large amounts of static. I'm by no means any type of audio or electronics wiz so it's still a work in progress for me.
On a side note, I have also just recently jumped ship over to the Lionel Legacy system, and so far I'm more than impressed!!! From what I remember from the old Cab1 TMCC days, Lionel has made huge strides in their offerings. This is just my opinion, but I think their steam sound sets are leaps and bounds ahead of MTH, their diesel sets are comparable if not better, but that being said I also wish I could get increased volume out of the Lionel prime mover and chuff sounds also.
Scott