Well!!! It seems I've been researching this forever instead of listening to music.
But, alas - still no answer. It is epidemic, however. Folks everywhere are writing into forums and asking "Why no bass?" -- and a common response is buy an outlaw icbm.
However, I did write into a
home theater magazine and got a response which I don't think addresses the problem.
I've concluded the two systems (Dolby/THX and SACD/DVD-A) cannot coexist on the same receiver with a sub. The workaround is to set up the SACD as a 5.0 instead of a 5.1 with large fronts. I suppose you could also wire the sub with high level outputs if you have small fronts.
It definately seems to be a hardware issue. I never got past the basic setup (white noise sound equalization). I can either balance the SACD or the THX but not both at the same time.