Bel Canto ref500 question


I am interested in the Bel Canto ref500 amp.  I see that the amp comes as a single stereo amp, or as monoblocks.

What are the advantages or disadvantages of one compared to the other?

Thank you!
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That is what I was trying to understand - whether there was actually a difference other than one box vs two.

Thank you so much
The REF500M monos are a step up from the REF500S stereo amp, but it has been a long time since I've compared the two that I can't fully recall the differences. 
Thank you for your reply!

I will take a look at the ref600.  I'll almost certainly be looking for used goods, for reasons of price.  Don't know if there are many examples of the ref600 on the used market...

Mostly I was trying to understand if there was a significant difference between the ref500s and the ref500m monoblocks

Thanks again!
Currently, they are only building the REF500S stereo amp. The REF500M have been discontinued for quite a while already. The more recent REF600M are quite a step up from the former REF500M.