Hi Fred... for clarity's sake my comparison to the M50's was based on driver configuration / specs. I couldn't tell you sound-wise cuz I haven't heard the M50's.
I consider the Advents to be a forward-sounding speaker... so since some others on this forum have said the M50 tends to sound laid back in comparison to M60/M80/M22 I recommended the M22/M60 to you. Although I'm sure the M50 is an excellent speaker (and would be an absolute step up), if you like the forward sound I believe the Advents have, I think my suggestion will work a little better for you.
The M22 / M60 are relatively easy loads to drive, so essentially
any receiver with the bells/whistles/features you're looking for
will drive them well.
Have fun tomorrow!!
