4.1 system with ceiling speakers

Music is important to me and so I'm thinking of running two Amps, one feeding a pair of Sonance ceiling speakers in the rear and the other a pair of 3s or 5s as a front pair.
There's some misunderstanding here, assuming by '3s or 5s' you mean Play:3 or Play:5. The Amp is for driving passive front L/R speakers. You can't use Play:3 or Play:5 for this purpose.

• Do I definitely need two Amps? Is there anyway of configuring the wireless speakers to be a front pair and the wired ceiling speakers as the rears?

See above. The front Amp drives passive speakers. You'd need two Amps.

• If I do run two Amps do I just run the TV through one of them via HDMI ARC?

Yes, the front one.

• Can I plug a turntable into one Amp and a CD player into the other?

Yes and no. Only the front Amp has an active Line-In. The other Amp, driving the surround speakers, disables its Line-In (and subwoofer) sockets when in this mode. You'd need a selector switch in between the turntable/CD and the front Amp.

• I have a satellite box and PC feeding the TV, am I right in thinking these sources will play through the system OK via the HDMI ARC lead?

Yes.

• Can all of these sources (Satellite, PC, CD, Phone) be streamed to Sonos speakers in other rooms

Yes. Note that any audio coming via the TV input will experience a slight delay in the other rooms.

• Will the Trueplay app work properly even though the sub would be wired? If not do I run Trueplay for the two Amps (wired and wireless pairs) and then just plug in the sub?

Trueplay is only supported on the front Amp when it's driving Sonance Architectural speakers, not any others. The rear Amp can however be coupled with any speakers and Trueplayed in conjunction with the main home theatre player, as it's only dealing with surround audio. You don't Trueplay front and back separately. You'd best refer to https://support.sonos.com/s/article/3222

• What's the quality gain in going from 3s to 5s for the front pair? Is the extra outlay worth it?

See above. You can't use Play:3 or Play:5 for this purpose.

Yes, I meant Play:3 and Play:5. Is there no way of running a pair as front speakers in a 4.1 setup with an Amp + passives as rear?
No, because there wouldn't actually be a home theatre player in the mix, able to receive and decode 5.1. (The rear Amp doesn't count, as it's basically a slave.) The home theatre players are Amp, Playbar, Playbase and Beam.

If not I could retain (and maybe upgrade) my existing passive fronts, with the benefit of the virtual centre. In that situation I presume I’d be able to run my wired sub from the front Amp, which would also accept the phono and CD inputs (switched).

Yes indeed, that would work, but as I indicated above you wouldn't be able to Trueplay anything.

You might like to browse the Amp user guide at https://www.sonos.com/support/en/sonos-user-guide/index.html#t=sonos-user-guide%2Famp%2Famp.htm

If I went away from home theatre (fronts/backs) could I just run Amp + passive stereo pair + wired sub and 2 x wireless stereo pair in a group? TV, CD and phono to the one Amp.

I wouldn’t have surround sound but I think I’d have an immersive setup that worked well with TV and music. I don’t actually watch many movies with planes zooming over my head, just broadcast TV.
In fact you would have surround sound. A wireless pair of Play:3 or Play:5 would be 'bonded' with the Amp, as the surround channels. They'd be subsumed into the Amp's room.

('Bonding' is different from 'grouping'. A 'bond' is a semi-permanent combination of players which all operate as a single room. A 'group' is a temporary, ad-hoc joining together of multiple rooms.)

As it happens you would not want to group the rear pair with the Amp, since they wouldn't play in sync for TV audio (but would for music). This is for technical reasons related to lip-sync and network transit times. You'd actually want to bond them as surrounds. A bonded setup always plays in sync.

And...if there’s no possibility of running Trueplay in a 2 x Amp setup there’s no advantage in choosing the Sonance ceiling speakers for the rears? Is not having Trueplay a big loss to the sound quality?

Trueplay is a nice to have, but by no means essential. Without it the Sonos app still allows you to control relative surround and sub volumes, and apply traditional EQ.

I think the problem though is that the Play:3s or 5s would be either side of the TV while the ceiling speakers are behind the listener so the room would be the wrong way round?
You spoke of "Amp + passive stereo pair + wired sub" so I can't see the point of putting the Play:3/5s at the front as well. Logically they should go just behind the listener, off to the side.

is a workaround to always set the wireless speakers in Full Stereo mode? But would I need to select that every time if the TV reset it?

With them at the front? It would be pretty odd, having them as surrounds alongside a pair of passive front speakers. The 'Full Stereo' option only applies to music, not TV, so surround noises would be coming from the front. And it doesn't change on its own, if that's what you mean by the TV resetting it.

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Stepping back, you originally wanted to involve rear ceiling speakers somehow. To do that you'd need an Amp. That rear Amp could 'bond' with any front home theatre player:

• Amp + passive stereo pair + wired sub
• Playbar (+ optional Sonos Sub)
• Playbase (ditto)
• Beam (ditto)

Been thinking about my options again and have a couple more questions, hope someone can advise.

An Amp can drive two pairs of speakers in parallel, so I could use one to run a front pair either side of the TV plus a pair of ceiling speakers at the back of the room, ie 2 x left and 2 x right. I’d also connect a wired sub. Presumably the Amp would create a virtual centre in each stereo pair.

I realise I wouldn’t have surround sound but what would the overall quality of that setup be?

Alternatively if I did use a Playbar/beam/base plus Amp and wired ceiling surrounds, how would I connect the phono?

Thanks.