New or Used Amplifier

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

used all the way.....the depreciation of that amp when purchased new makes buying used a much better bet.

Thanks everyone for the comments. Can you recommend a speaker wire for this length.

I will look for a Multi 3 since I am going to 5.2 or could I get Multi 5 and only use 3 outputs.

I agree, used would save you a ton on money.

Your in-wall installation (asssumed so) is going to have to be fire rated speaker cable or your insurance policy exclusion clauses be come an issue.

Because

(I) it is the just the rears and surrounds on the long runs, AND
(II) you are using a hi-quality build amp to drive them,

the BELDEN line (a range of quality and gauges) will serve very nicely IMO. I used them to surprisingly good results on the advice of the Dealer for long in-wall runs.

Alternatively I wired the next room with Van Den Hul.... more expensive but I did not see any improvement over the cheaper Belden .

Center channel .... a different story here: a hi-quality speaker cable required to match you hi-quality LF and RF cables is strongly suggested to aid in getting that seamless soundstage across the fronts. Don't cheap it here.

ICs: I started the HT expansion journey with NORDOST FREYs that I still have for L-F 2 channel. I then went to NORDOST HEIMDALLs for all of the the centre, rears and surrounds.

Good ... you betcha ..... BUT ..... the AVP had the usual cheap stamped nmtal very crowded back panel and comparative cheap usual connectors that made the locking WBT RCAS on the ICs a big hindrance.

I went with ATLAS All-CU Navigators and then to REGA COUPLE ICs. The REGAs are the Goliath killers and for conveying the purely manufactured signal in the rears and surrounds. they are my choice as superior top performance at a good price.

Their performance is way above its weight class and the Neutrik Profi RCA connectors are outstanding and arguably on par (at least) with any of the WBTs for this selected performance criteria ,

The centre channel IC is still NORDOST to match the LF and RF.