If 2-ch is your priority I would do it differently. I would buy a 2-ch only preamp with unity gain input/control for pure 2-ch playback. I would keep the Yamaha as surround processor and connect its two front channels to the preamp. With this setup, you will get the best 2-ch playback without having two separate systems. No matter how good analog pass through is, a surround processor cannot complete with the best preamp at the same price.
There are many great preamps to choose from in the 3-5k range, both tube and ss. If you are willing to buy used, you can even get some top-of-the-line state-of-the-art ones.
BTW, I have a Yamaha DSP-A1 connected to a BAT VK-50SE. In a direct comparison, it outperformed a fully loaded Theta Casablanca in 2-ch.
There are many great preamps to choose from in the 3-5k range, both tube and ss. If you are willing to buy used, you can even get some top-of-the-line state-of-the-art ones.
BTW, I have a Yamaha DSP-A1 connected to a BAT VK-50SE. In a direct comparison, it outperformed a fully loaded Theta Casablanca in 2-ch.