I’ve had both in my system some years back although the MC2102 was on a home audition basis for a few weeks. The 501 monos were in my system for a few years.
It’s personal preference of course and system synergy comes into play but to generalize, you would be giving up a lot of power/reserve so depending on speaker loads you may give up some dynamics.
The MC2102 was a softer, relaxed and more laid back sounding amplifier. Almost too much so for my taste but my speakers were also presenting lower impedance load than a tube amp typically likes.
You would also be giving up solid state “day to day“, “year after year“ reliability for an amplifier that will ask to be fed new tubes every so often.
If you just have to have tubes, the MC2102 is a solid choice but I personally do not think you would gain anything at all compared to MC501 which are a very smooth and liquid sounding solid state amplifiers to begin with. I wouldn’t trade.
