New or Used Amplifier

For HT.....used.

With your YBA gear, I would suggest that you keep it in the same YBA designed family and go buy their used Audio Refinement Multi amps. (YBA designed but made in China line-up)

They impressed me enough to buy their 3 channel and the separate 2 channel (both used) to incorporate in HT. They serve as the centre channel, reads, and surround amps. Their superior build quality bested the top CAMBRIDGE AVR that I sent lacking. They now mate perfectly with my primary 2 channel for audio integrated amp with its direct pass-through (REGA Osiris ) as the LF and RF when I need it for HT.

Google the AR stable of amps, If memory serves me, they also had a full 5 channel.

Thanks for the suggestion and will take a look. The speaker wire length for rears is about 55 ft, so I ran Mogami interconnects for rear channels in walls already. I was told a 55 ft run of speaker wire would cause problem for amp. I was thinking of separate amp for rears and center.

The speaker wires length is not going to hinder you
I ran about the same length (up the walls, the length of a long room in the ceiling , down the walls plus the hookup lengths) without any difficulty.
I use the 3 channel amp for the centre channel and the rears, the two channel for the side surrounds.

The separate preamp processor is the " disposable" part, to be upgraded in the future as the codecs change.

Recommended : NuForce AVP-18.... Fully digital with all HDMI (no legacy inputs ). Google the reviews - highly recommended .... Especially with the ARCAM Bluray player to round it out.

Canuckaudiomart has an Audio Refinement Multi 5 and a Multi 2 listed for sale