Levinson 300 series versus 400 series amps

I'm particularly interested in how the ML 334,335,336 stereo amps differ sonically from the newer ML 431 & 432 stereo amps. I realize there have been some posts on this subject, but usually people just say "X blows away Y". Instead I'd like to read more detailed comparisons.
I heard a system with late-model 300-series and a set of brand-new 400-series monoblocks, and I couldn't tell the difference between them. AFAIC the difference is the 400-series are lighter, more compact, and put out a bit less heat.
the 400 series is mostly for multichannel and it cost more because is new i have a 333 and it sounds wonderful and can drive any speaker no matter how difficult the load is also the newer 336 also sounds great enjoy the music