In answer to the 555 running with a single centre speaker - pretty positive you can’t bridge to mono so I think you would only run one channel i.e. left OR right signal, in and out. Not sure that’s the smartest thing to do though and you might want to consider a mono block? 505s are rare I think but the even older 205s do seem to pop up from time to time. Or just run with a phantom centre before making any final decisions.

Re reading your original post room correction seems really quite important as does budget. I’d perhaps look at other separate room correction options which then sit in the final signal path, like a MiniDSP, then tag on a processor. I’ve not tried the MiniDSP; I am playing around with Roons PEQ at the moment and if that is anything to go by, it’s pretty useful. I’ve not had time to use my Dirac option yet....

Not sure of prices for a 501, you could search eBay sold prices as a guide. No bad thing to give away but it is certainly worth something.


Main: Marantz SR8015 / Polk Audio Reserve R500 / Bang & Olufsen Beolab 4 / Arendal 1961 1V / Oppo 203 / WiiM Pro Plus / Apple TV 4K

Spare: G68ADV, HD621,DSP5000.2 & DSP5000.2 HC. ATC SCM20PSL, C3C. Rotel RMB-1077. Bang & Olufsen Beolab 1 & Beolab 7.1. Kef Q150. Dynaudio Xeo 2.