Does the Mark Levinson 331 suck?

Levinson amps are nuetral. They reflect the source and wiring. Another factor amps like the Levinson, Krell, Halcro and many others, with large crurrent capacity, don't start sounding their best unless provided with a seperate 20 to 30 amp circuit just for themselves. I've not had experience with the Marsh so can't comment. Auaarons is correct: without knowing your system configuration none of us can really help you get better sound or figure out what's going on.

I had one and really liked it in the beginning. I then started listening to other amps and found mine bright, hard and the fatigue factor was bad. I switched to Mcintosh in SS and tube and have never looked back.

By the way, I installed a dedicated 30 amp line specifically for the 333 when I bought it.

Obviously you need a tube amp. Ah warm , musical, distorted and with flabby ass bass. I love the "27 sounded better than the 331", sounded like a tube head. Keep your crossover distortion if it makes you happy. Come on people at least admit that warm and musical (the way talked about here) are distortions not there at the input. I guess real just does not sound alive anymore. There is not much about ML that sucks in my opnion and Richard Marsh very fine designer that he is is just hoping to get a copy of Mark Levinson's design books. THe 331 is a true voltage and current source unconditionally stable into 1 ohm. The Marsh is power supply limited into 4 ohms at the rails. The 331 is on the order of about 100 times more linear and quite than the Marsh. Something else is worng.
Frog

The only part of my system that has remained constant over the last 2 yrs are my ProAc Response 2.5s. I have used Copland CTA-402 integrated (tubes), Plinius SA-100 mkII, Pass X250 and Sonic Frontiers P2. Now owning a 1996 vintage ML 331 I can state that this is the best match yet. The 331 is neutral but has so much better bass control and micro detail that in some case, I am hearing old music for the first time. The soundstage is so much wider and deeper. More air and placement between instruments. I will be keeping this system together for a while.

ProAc Response 2.5s
ML 331
CJ PV-12 w/phono
Metronome CD2v Sig