Starting from scratch and say $5000

I am not inclined to make a specific recommendation at this time. That said:

In your position I would consider an integrated amplifier. There are many great ones available that would fit into a system supported by your budget. 

I also would consider exploring the speaker market prior to considering amplification. Consider speakers that are not difficult to drive, having a reasonable sensitivity and impedance curve across the frequency range. The choice of amplifier is often driven by the speakers under use.

You didn't mention what sources(s) you will be using. What are they?

got it. btw, the links to harbeth and spendor on your site need to be updated (dead end now)

just recently re-connected analog sources (cheap cd/turntable/tuner) but likely to stick to most common source of streaming currently handled by analog Sonos out. I have toyed with pc streamer idea, trying to consolidate gear for long term. I do miss and have enjoyed pulling out a cd but going through process of making sure they are all lossless ripped before I can the old iMac or use it as music server (that it has done fine with sonos for 15 years, but yeah, long in the tooth). I guess that enters the discussion too, how badly am I going to hang on to an FM tuner. I am lucky now to be able to pick up the digital signal of WWOZ New Orleans and the classical WWNO.

forgot to add that sonos had digital out and same for even the cheap cd transport so a dac may be in future, either in an audio component (pre-amp or direct-to-amp) or as part of pc rebuild. Even downgraded by the over air old radios and dacs in the sonos, Tidal or Radio Paradise hi rez audio sounds pretty darn good compared to old mp3 compression. 

Just to throw it out.... I would look at:

• Magnepan .7s at ~$2000
• D-Sonic  M3a-800S Stereo Amplifier (400x2 into 8 Ohms but stable down to 2) at ~$1475
• MiniDSP SHD (Streamer, pre-amp, DAC, lots of DSP options for bass management) at ~$1299
• SVS SB2000 Pro - ~$899

Total Price ~$5673.00

This is all priced as new and I think you'd have a very nice sounding system.  Add a subscription to Qobuz and a NAS with your own CD rips and you'd have tons of music at your fingertips.  

The issues with the above suggestion are:

• MiniDSP SHD can be a great streamer/preamp, especially if you want to use custom crossovers for managing a single or dual subwoofers.  It even comes with DIRAC I think if you wanted to use room correction.  But it would not be as "plug and play" as a traditional preamp.
• In addition, the MiniDSP SHD only has one analog input so you'd be limited on your sources.  You could add a turntable and just use that as well as streaming.  It does have a few digital inputs, though.
• The MiniDSP SHD would probably convert a turntables analog signal into digital so if that bothers you, it's not a good choice.
• You'd need a phono preamp to add a turntable, either built into the turntable or external.  Schiit makes one for about $150 I think.  
• You'd need a room that has space to support the Magnepans.  Generally they sound best when you can bring them out into the room a few feet.  So if your listening room is shared with other things, maybe not the most convenient option?
• You'd have to like Magnepan speakers.
• You don't need the sub.  But, then again, you may want two.  Just depends on if the Maggies satisfy your bass requirements.
• You'd have to like the DAC in the MiniDSP SHD.  It is apparently very good but some people feel strongly about their DACs
• The MiniDSP SHD uses Volumio as the streaming software.  I've used SONOS and BlueOS but not Volumio so I can't give you any opinion on how user friendly that software is.

FYI, right now I'm using a SONOS Port into a Schiit Modi3 with each channel going into the input of an SVS sub and then running the output of the SVS sub into one of johntwo D-Sonic mono power amps into some Maggie MMGs.  Sounds good to me.  I do have some 1.7s on order and will probably replace the Port with that MiniDSP SHD in the near future.

Good luck!