This is one of those great, unanswerable questions. It attempts to compare not only apples with oranges, but pears with bananas too! There are too many unknowns here for any kind of definitive judgement:
The C1.2 Mono is a very different animal to the C1.2. Adding the X1 power supply to the equation further muddies the waters. In a six-box set-up, there are various ways of configuring the power supplies: do they have single or dual outputs; do they drive just the transport and head unit, just the DACs or all four? Each option delivers a none too subtle difference in performance. So, for example, in a twin or dual single supply situation, I would choose to feed the transport and head-unit - but that's because I have the temporal and dynamic authority from a line-stage to back up the digital front-end. If I was driving a power amp (or amps) direct, I'd use the X1 outputs on the DACs...
@RoyGregory - I can't thank you enough for sharing with me your time, your knowledge and experience, I'm extremely grateful. Especially with all the variables your input is priceless.
Let me try to put things into more perspective and remove some variables.
It's not finally decided yet, but the chances are that I have to move my system from a dedicated room to the living room. That means less space for the system and WAF will come into play. That means further the less boxes the better, at least for my wife

. Yet we didn't even speak about the amps and the speakers
And here's a short overview of my system:
1. One dedicated line goes directly into a 10x power distributor from S.I.N Audio.
Another dedicated line goes directly into a Synergistic Research Galileo SX ground block. The complete CH setup is connected to the ground block, only the C1.2 head unit is connected with signal and chassis ground.
Both lines are terminated with a Gigawatt circuit breaker.
2. D1.5 is connected to the C1.2 via HDLink connection and a clock cable over the Sync I/O boards, the C1.2 as clock master.
3. The C1.2 Mono was originally a C1 Mono which was fully upgraded around a year ago.
4. The 2x X1 have both dual outputs. One X1 feeds D1.5 and the C1.2 head unit, the other X1 accordingly the two DACs.
The DACs and the X1s have underneath Symposium Rollerblocks (double stack) and are placed on Symposium ISIS racks
5. D1.5, C1.2 head unit and the ground block reside on an Artesania Exotery rack with Carbon Fiber Linear Arms. The D1.5 is placed on an extra Symposium Quantum platform, the C1.2 head unit on a Symposium Ultra platform. Both CH units are equipped with CH titanium spikes from the 10 series on copper spike shoes.
6. 2x M1.1 in Mono mode with 10% Global Feedback and -3 Gain. Both amps are placed with their composite spikes on copper spike shoes onto Symposium Ultra platforms which sits on Artesania Aire floor platforms with Carbon Fiber Linear Arms.
7. Speakers were originally YG Sonja 2.2 and were fully upgraded to the new 3.2 version last year. This new 3-series is a completely different beast and needs a lot more care with room-setup because of the stronger and deeper bass.
Attached are two pictures of my system to get a better impression.
The complete system is placed between the speakers and I'm aware that it's not ideal.
The music I like goes from early music interpretations with Accordone, Christina Pluhar, Jordi Savall, etc, also classical and baroque music from Beethoven (btw thanks for the recommendation for the 9 symphonies with Jordi Savall), Mozart, Stravinsky, Bach, Vivaldi, etc. up to 70ies japanese Jazz with Tsuyoshi Yamamoto, Isao Suzuki, etc. and also 80ies and 90ies music from my youth with Eurythmics, Depeche Mode, Yello, Art Of Noise, Laurie Anderson, Kraftwerk, Portishead, Massive Attack. And there's also PJ Harvey, Lamb, Soap & Skin, Roisin Murphy, Ryuichi Sakamoto, etc.
Of course as you wrote I can't and don't expect that a single box solution will match the 6-box rig. But if the Studio Player can bring other rewarding elements then it's worth to really take it into consideration. And hopefully there's even room for a preamp, let's see. If I understand you correctly, a capable preamp could bring more detail and intimacy into play in conjunction with the Studio Player?
And also the external power supply could change the balance considerably.
It's really very tempting to go this route and 3 boxes are still better than 6 boxes
And thanks a lot for your preamp recommendations. I'm aware that a L1 would be a great choice, especially in conjunction with the M1.1 and X1. With X1, it's getting big again with 4 boxes. I'll look into your other recommmendations which some I don't even heard about.

