Both my HTS 7.1 and my S1200 had modified/recapped power supplies. These units use the Krell fully discrete Class A audio circuits and they both have shunt regulated power supplies. The Class A circuits require a lot of current and It is my opinion these two units have undersized power supplies. With stock units, you may find that these Krell processors sound rather thin/bright (lean bass with a sharp mids/highs). There really isn't enough capacitance in the power supply to keep up with this and the audio circuits are starved as a result. Increasing the power supply capacitance solves this problem.
The S1200 does not have ARES room correction. However, it does have a Room EQ where you can apply up to 3 filters to each audio channel. Several filters are available: High Pass Filter, Low Pass Filter, Notch filter (like a conventional EQ), Low Shelf Filter, High Shelf Filter, Peaking Filter (parametric EQ). I do not use EQ except for applying a Low Shelf filter at 25hz so that my subwoofer does not peak.
Another thing. There is a known problem with many S1200 units where the DSP board has a hardware failure. This can be shown as unstable audio when decoding Dolby/DTS from HDMI input and other things like DTS-HD bass management, loud beeps/clicks, loud static when changing video resolution formats, inability to decode Dolby Digital Plus, etc. The solution is to send in the S1200 to Krell so that they can replace the DSP board with a new one. I'm not sure about the cost of this as my unit was still under warranty.
If you are willing to solder in some large capacitors onto the S1200 power supply, then the S1200 will likely be the best sounding processor out there. Of course, 4K and HDR are not supported.
However, if you want 4K and HDR, the Foundation is likely one of the better sounding units.