Re: At the crossroads... advice?
The biggest problem with the 900 DR is just what you discovered: it doesn't do low volume distortion well at all because of the diode clipping preamp and the fact the best tone comes from the power tubes when you blast it. Both the DSL and JVM do both bedroom and high volume quite well. A pedal in front of both your 800 and your Super Bass should sound amazing, don't discount that option. For new amps, also consider a Haze or Class 5.
The DSL is by far the least expensive way to go (outside of a pedal and maybe an EQ) and it's just as good as the other Marshalls; the JVM is the most expensive but also has the most features. But let your ears be your guide; you'll be happiest in the long run that way.
1999 Marshall DSL 50
Music Man 65 Reverb late 1970's (?)
Late 1970's (?) Fender Champ
Marshall battery amp
1980 Model 1982A 4x12 cabinet G12H-80's 444 cones
1983 Model 1982B 4x12 cabinet G12-80's 444 cones
PRO 4x12 from the 1970's
1976 Les Paul Standard
Epiphone Les Paul knockoff
ESP Lawsuit Explorer
1979 Chiquita Travel Guitar
1995 Taylor 310