Amplification Recommendations For Magnepan .7

Yes you can.  The SVS2000 only has line level inputs (no speaker level), but it also has an output.

You would run a pair of interconnects from the output of the Aune to the input of the sub.  Then run a pair of interconnects from the output of the SVS2000 to the Bryston.

The SVS2000 has a fixed 80hz/12db per octave high pass filter.  That should work pretty well.

You could also run a set of RCA "Y" adapters out of the Aune, one to the Bryston and one to the SVS2000.  This will work, but might cause some impedance problems.

The Yamaha X675 receiver I used had Airplay built in to it. It also had bluetooth. I used to use Spotify that could play through either bluetooth or Airplay. I switched to Tidal and I think it only works on Airplay.

I am going to use the Aune X1S headphone amp that I already owned as the preamp and DAC. Here's a link to the amp front and back.

I would like to know what I ought to get that will allow me to deliver Tidal from an iPhone to the Aune. I assume it's an airport express. Is the Aune going to be able to be my preamp with the sub and the Airplay? I would like to know if that's exactly right and if there are alternatives to the airport that could give me a better quality sound. The Tidal is supposedly lossless and CD quality. Would some of that be lost with the airport and is there better? I've spent almost all my budget on the amp and speakers. I would like to find an AE alternative that sounds great but isn't more expensive than $250-300.

Are the outputs of the aune fixed or variable? 

Okay, so I don't think that it's really that safe to use the Aune X1S amp/dac as the preamp.  If I have to use the source (computer or phone) to control the volume I'm concerned about blowing out the speakers if not careful.  I let my 13 yo daughter play her music and she's responsible but it's too risky.

That being the case can you recommend a DAC with volume control thats not too expensive?  I would want to be able to get a wireless receiver that I can use with Tidal.  Tidal is compatible with Sonos, Bluesound, or Squeezebox.  While I'm at it, is Bluesound and Squeezebox better than Sonos and which is preferred?

I now own two amplifications:
ARC LS25/II + 100.2
and
Accuphase E-360
I will have to make a choice between them in the future (it's more a choice between separates and integrated, actually).
I already drove MG12's with the 100.2 and I liked it.
so my question is:
what about the 0.7 with the ARC 100.2 ?
and what abvout 0.7 with Accuphase E-360 ?

I've never heard 0.7's, except for a very very very short listen in a shop; in that circumstance, power amp was an Accu A30, and I liked it, but listening time was really far too short to be meaningful.