Your setup asks for an ADI-2/4 Pro SE, which can easily managed all your connections.

Here‘s an overview how to connect all your sources and speakers, preferred connection marked bold.

• Rega 6 turntable > ADI-2/4 analog in using RCA to TRS adapters (see below).

• Yamaha CD-S 1000 CD-player > ADI-2/4 Coax or Optical digital in.

• Minimac Streamer > ADI-2/4 USB in.

• ADI-2/4 analog out 1/2 > (RCA in) SVC subwoofer (RCA out) > power amp > main speakers.

• ADI-2/4 front PH 3/4 > optional headphones, if you like.

No, left stays left, right stays right, all through.

On both subs you will use the left in and out only, and leave the input marked as ”LFE input” alone.

ADI-2/4 left out > left sub in > speaker amp left
ADI-2/4 right out > right sub in > speaker amp right

If you buy two subs - which I consider a good idea - get cables that are not fitted together as a pair if possible (a bit hard to find for a reasonable price).
Or you just split the RCA side long enough to reach both subs, using a cutter knife.

ADI-2/4 Pro SE’s Rear TRS are a versatile 2nd output that can carry the same signal as the main out 1/2, or can be assigned to the secondary channel 3/4’s signal.

I DO NOT advise to connect the subs to those, because:
- it makes the sub’s handling complicated,
- you would miss the sub’s frequency management for the main speakers, it’s 80 Hz high pass filter.

The SVS DSP's AD/DA conversion is really not great.

These subwoofers are meant to be used with an AV receiver/pre with separate outputs for LFE and speakers, using the bass management of the AV receiver/pre.

If you connect the ADI-2/4 PRO to the subwoofer's inputs and the speakers to the subwoofer's outputs you will sacrifice a lot of the (extremely) high quality of the ADI-2/4 PRO.

That would be a shame, loosing quality. Its what makes my speakers shine. Any suggestions/alternstives allowed? Other subwoofer? Thank you

Full range loudspeakers don't need a low cut, only the sub for itself needs a crossover cutoff.  The stereo signal has to be forwarded untouched !

Don‘t complicate things here, please.

I gave my best to keep it simple for @woug68, who already mentioned that the info he collected feels overwhelming.

I do not see a filter for the main speakers mentioned in it‘s manual, but most SVS subwoofer have it, so I assume there‘s a simple passive one.
If it was DSP it would certainly be accessible by it‘s app.

Anyway, the setup suggested will work nicely either way, specifically with two subs.

@woug68:
If you like you can ask SVS if and how the line out is filtered.
These are the possible options:

1. Direct wire linked (likely).
2. Electronically buffered unfiltered feed through (unlikely).
3. Passive high pass filter - one cap, one resistor (likely, assumed).
4. Active analog high pass filter (unlikely).
5. Digital DSP high pass filter (very unlikely).

Well, you can't be always right. ;-)

The SB 1000 PRO is a DSP subwoofer as well (and controllable via app).

and has no DSP either, those potis and the overall layout is the typical analog sub for HiFi stereo set.

@wough68

Once you have the subs there‘s a simple test:
Switch off their power, if no signal is going to the main speakers any more, there‘s some electronic in the path that should be bypassed.

To do this, just use this type of splitter cable to avoid running the signal through it.

The RCA male goes into the sub, the two female RCA‘s go (with the cables already mentioned) to ADI-2/4 and the power amp (as simple, sound-neutral wire link).

It’s a 6 bucks invest.
My bet is, you won‘t need it

I am quite astounded that you discuss that openly here. Very nice. To someone like me it I deed daunting this hifi hobby. I am very grateful for a forum like this. To really understand it all I will need some time and some learning. But this helps A LOT. So thx to all. If I don't react it is not out of indifference. It is purely because like everyone I need to work and absorb and process the info. It can be an expensive journey. But it can be worthwhile. Though my ears aren't the best anymore, music is so much more on a decent hifi installation. It is not trivial to me.  It is a soothing experience. Again. Thx  you all for your advice and patience!