Jim,
If you're looking for an excuse to get a new amplifier for your system, many of the contemporary 5.1 (or fancier) receivers/amplifiers have a "night mode" or "dynamic range compression" (D. RANGE and D. COMP in Sony menus) that do what you want. E.g.,
formatting link
. Unfortunately, this feature usually doesn't make it to the short "feature list" of most receivers because it's nowhere near as sexy sounding as 192kHz
24-bit 7.1 sound reproduction or somesuch.
What amplifier do you have now?
---Joel