Still experimenting with various pre-amp/amp combinations and will post further impressions once I receive balanced/XLR cables.
UPDATE: To backtrack a bit. Prior to purchasing NuPrime products, I had quite sorted sound system, that suited my musical tastes and my budget. Namely, Monitor Audio GX 200 speakers, Yamaha A-S1100 integrated amplifier; analog sources Rega RP8 turntable, Ortofon Quintet Black S, 2M Black, Kontrapunkt b, Denon DL 103R cartridges, Pro-ject Tube DS phono stage; digital sources Yamaha CD-S1000, Cambridge Audio StreamMagic 6 DAC Steamer via couple of WD NAS drives. Mostly listen to chamber jazz, classical (minus opera) and am fond of electronic music as well (from Tangerine Dream to recent like Asura, Aes Dana, E-mantra etc.). As I grew up with mother playing violin and older sister piano (we had Petrof Grand in the house) my taste in sound reproduction is decidedly of intimate, chamber kind.
The only piece of equipment listed above not realy to my liking was CA Stream Magic 6. It gave off too edgy and somewhat harsh sound. Hence I have been looking for a DAC that will be closer to my taste in sound. My budget was around $3000. I have than auditioned five or six in that price range until I stumbled on review of NuPrime DAC-9 and tried it out as reviewer described exactly the sound I was after. It took me about two hours of listening to it, to decide to purchase. Most of those two hours I spent wondering about quality of the product, considering its price point which was out of sinc with sonic performance I was experiencing.
Obviously I was intrigued about the brand and did some internet research including posts of this community. After which STA-9 and ST-10 landed in my system for evaluation, impression of which I described in one of the other posts above.
ST-10 is impressive amplifier and since purchase, I am using it in bi-amped configuration to run LF. Still prefer Yamaha's A-S1100 reproduction of MF/HF, it sounds more "true to life" for me. I am also using it's pre-amp section. DAC-9 is only used as converter (via Roon Server running on Windows 10 using ASIO driver). What is very noticable, since ST-10 took over LF duty, Yamaha's quality in reproducing mid and high ranges is of entirely differentint quality. Having magic in low and mid bass, sprinkled pixie dust in higher frequencies as well.
Now that I have balanced cables, I could fully explore other combinations e.g. DAC-9 as a pre-amp in bi-amp configuration, again ST-10 running LF but now on the balanced line. (Yamaha having only single ended inputs remained in RCA line).
After listening few tracks, using this balanced line configuration for ST-10 and DAC-9 as a pre-amp, I can only find one appropriate word for the bass experience... brutal! It was so powerful, I felt impact inside my rib cage and all this at mid volume listening levels. This LF reproduction is so overpowering of the overall music reproduction, even being also very accurate and without any trace of boom, that I will not be able to keep this setup. Remember, my Yamaha amp handling MF/HF is on a single ended line, and is just swamped by this ridiculously extended bass.
Now I have to wonder, how would 2× ST-10 sound in bi-amped configuration, both running balanced lines? NuPrime, I hate you