It was the output tubes all along...

@mijostyn Thanks for taking the time and effort to help me improve my system.  I don't do any sound measurements, but it's clear that you have mastered the process. I actually believe everything you are saying.  Initially, I was entertaining purchasing the Magico subs until I saw the financial damage that would be incurred! What was presented primarily then by Mike was the Titan series.  The size and pricing for 2 units didn't make sense at that time.  More importantly, my overseer and CFO felt much more strongly than I did on that matter.  The swarm was an attempt to add something at a low level of risk.  I think I got my money's worth out of them, but I suspect you're right about them being underpowered for the S7's.  It would be great to be able to do an in house sub audition, but I don't think that's easily arranged.   We had an art dealer for a while who knew our house and interests verry verry well.  He would occasionally drop by to show us a piece.  He would do a quick walk through, rearrange some art and leave a space for the piece he brought over and told us just to "live with the piece" for a few weeks and see what we thought.   Oh, if I could only do that with subs.  The S series may be the ticket though. 

In answer to your questions, I have an old Sony SACD and Meridien cd player, but they are over 20 years old and don't see much play.  Meridien died and I don't see the benefit of a repair.  I should have Modrighted the Sony.  BTW, I have a TON of cd/sacds.  I don't have any organ music recordings, but I see where you are going with that. Thanks again for your suggestions.  You definitely got the sub gears whirring in my head.

The issue for many audiophiles is digital phobia. They stubbornly want to keep their system pure analog in the belief that it sounds better. In reality the benefits of moving over to a digital preamp/processor are legion. Conversion to and from 24/192 digital is now invisible. Once you are in numbers you can do almost anything without added problems such as subwoofer management, EQ, room control and high resolution steaming (Qobuz). The benefits for outweigh any detriment if there even is any. The best digital preamp for you would be the DEQX Pre 4 which is still in Beta mode, but the prices are still about 1/2 of retail. My friend with the S7s just got one. We have not set it up yet. The best value is the MiniDSP SHD. Down the line you can add a high end DAC for your VAC amp/S7s. The SHD is only 1500 with the best microphone. Add two Martin Logan Balanced Force 212s and you are in business for a total price of just over $10,000. The 212's are handily the best value in subwoofers today. With the SHD you only need a CD/SACD transport like the Bricasti M19. The SHD is set up to stream Qobuz which IMHO is the very best streaming service. It also uses Dirac Live, the easiest room control system to set up. My guess is that this addition will blow you away and you will wind up getting the DEQX which matches the quality of your system. It also has a fine phono section in it designed by Dynavector. It is designed to use a transformer for low output cartridges. I have a Pre 8 which is the identical unit , but with a 4 way digital crossover for people who want to triamp their systems. You can make any loudspeaker fully active. I would leave the S7s alone in this regard. Magico knows what it is doing. You want the Pre 4 which is somewhere around $7000 now and will retail for $10,000 I think. This would make adding subs a total of almost $20,000, but you won't need to buy a better DAC. Financial advisors always think HiFi is a waste of money. I do not bother mine with it avoiding the argument all together.  

When did this shift from rolling output tubes types to digital EQ and sources?

Anyways, I do agree with @mijostyn that a good ADC + DAC conversion process can be extremely transparent. Rather shockingly so. I’ve heard this by playing my vinyl setup through a Meridian 808v5 CD/preamp/DAC (which converts analog inputs to digital). I’ve considered continuing to use it this way for the excellent L/R balance control. Don’t mind the sacrilege. Still vastly prefer many of my vinyl records to their digital versions; it comes down to the mastering.

I’m surprised you find the need for subs at all on S7’s! They’re beasts, and rated down to 20Hz on their own. For music, no more should be needed, unless it’s some massive room? Adding extra energy down there will also add to the challenge of clean vinyl playback. You definitely DON’T want your VAC amps dealing with any subsonic feedback or rumble - it will rob their performance more than extension gains. Have you tried running the S7’s alone lately? Make sure you don't see any woofers flapping during playback. 

@orthomead There are certainly more august minds that have penned well reasoned advice above.

In the KISS realm a pair of subs with (say a pair of REL classic 99's that will run under 4k delivered) settings and placements fiddled with will yield an all enveloping sound even with the terrific Magicos.

Your listening room I imagine has all the treatments bells and whistles.

If you try the KT170's, then please check with the manufacturer first before putting them in. Not sure about how much space there is where the tubes go in your monos but the Kt170's are fatter than the KT88's.

@mulveling That 20 Hz rating is at one meter. They do better than most speakers, but the issue is that you have to boost 20 Hz 10 dBSP to get the right balance. This will push the S7's woofers into their nonlinear zone at rock and roll volume increasing distortion. This will also torture the amp. Breaking out 100 Hz down to a dedicated subwoofer system decreases distortion in the main speakers and allows you to get the proper boost without torturing the main system.