The sonic signature of the S1200 is going to be very similar to the HTS 7.1, but better in my opinion due to supporting hi-res audio/bluray and a better digital section (Sabre DAC with TCXO clock). The HTS 7.1 was the first line of products from Krell where they made the analog circuits much higher bandwidth. This gave us a faster sound, faster attack, more clarity and detail. Some people also feel that it is too bright/forward sounding ("in your face" sound). I personally love this sound for both music and movies because it gives a sense of realism that warmer systems do not have. If this is not what you’re looking for, then maybe S1200 would not be a good choice.
The AVS / KAV300r / KAV250P were all older devices back when Dan D’Agostino was influencing the design and all had a warmer and more laid back sound. I have found that Dan likes designing towards a warmer/richer sonic signature. While you could use a combination of these three preamps to handle the analog output of the bluray player, it is going to be nearly impossible to match the volume output of each as you turn the sound up and down during different movies/music (each preamp has a completely different volume indicator and may have different steps). For example, even having the center channel 2 db less than left/right will cause vocals to sound very far away and hard to hear. If you wanted to do something like this, you would want 3 of the exact same preamps, such as 3 KAV-250P, so that you could use the same remote to control the volume steps. In addition, the analog output of the UB900 is going to be sub-par.
If I went that direction, I would want an bluray player with an extremely good analog stage, such as Oppo BDP-105 or something. You could also look at a 7-channel analog preamp, such as Parasound P7. This ultimately would be more money than buying a used S1200.
Since you liked the warmer/richer sound of the AVS, I would look hard at the Marantz AV8802/AV8802A as a modern replacement. The only difference is that the "A" model supports the new HDCP 2.2 protocol. The Marantz sound is slightly on the warm side of neutral, but still very detailed. Many people love the "musicality" of Marantz. It also has excellent power supply and discrete fully-differential balanced audio circuits (in case you want to use XLR cables). They are ranging from $2300 to $2700 used. There’s a 8802 on ebay now for $2300.
Alternatively, you could look at Marantz 7702/7703. They are cheaper and maybe more in your budget. However, the main power supply on these is half the size of the 8802 and the analog audio channels are all condensed onto one board. The 8802 has 13 individual boards for each analog channel. Sound quality is not going to be as good as 8802.
