Picking an amplifier

My experience with Sony was a long time ago. I remember thinking their receivers were very bright/cold/harsh. I think the "ES" level help smooth stuff out, but I always thought they were somewhat sterile, but very clean sounding. I suspect that the Sony fully discrete analog circuits, such your Sony DSP-EP9ES and also like those in the Sony HAP-Z1ES network player will be significantly better.  However, I don't think circuits like those would be in the Sony Receivers.  Also, Sony only makes receivers.  They do not make HT Processors.  I do not have any recent experience with Sony, so I could not comment directly.  Only theorize.

One of the things I like about Marantz processors is that they have fully discrete output stages for their audio with a significant power supply to back that up.  The DAC I/V stage is done through an op amp with relatively slow slew rate (further contributing to the Marantz warm signature).  It is warm, however, lol.

Nope, I did not order the Musiland. Yes, I am currently running the Xonar Essence ST PCI version. I think I'm going to wait until next year and get these items:

https://www.shenzhenaudio.com/l-k-s-audio-mh-da004-dual-es9038pro-flagship-dac-dsd-input-coaxial-bnc-aes-ebu-for-dop-usb-i2s-optical-audio-decoder.html

https://www.ebay.com/itm/Pink-Faun-I2S-bridge-LKS-audio-Model-IV-Pink-Faun-IL3-I2S-HDMI-to-RJ45-cable-/281933158086?hash=item41a48696c6:g:wu0AAOSwUuFWvK9v

Based on everything I have read, the i2s interface is superior to COAX spdif. Since I don't care about DSD, this i2s card should work out really well. It's the only computer i2s card I know of and it does not support DSD direct. (I think I can still use DOP through Jriver).

Guess you'll just have to take a chance with your decision. On one hand, the Musiland has some pretty good hardware design approaches.  On the other hand, Xonar is excellent as well and uses power directly from the power supply (via a hard drive plug) instead of drawing power from the PCI slot like the Musiland does. With the Xonar, you are also paying for the DAC and analog stages of the sound card.  In any event, I'm sure it will be much better than toslink from the MOBO.

Bright / neutral / warm has more to do with how the power supply and analog stages are engineered. The choice of DAC chip has almost nothing to do with this. :)