I don't think that you will find what you are looking for in a different DAC. DACs are
meant to have no sound, they are
meant to be transparent. That's what they are designed to do. The SU-9n and the
D300 measure very similar. They both measure transparent and I would expect them to be exactly that.
The PCM filters most likely make no audible difference. At least for me they didn't and I haven't seen any indication that people could reliably discern between them in a blind test. But to be fair, I haven't looked for any evidence of this - maybe such test results exist and I'm not aware of them.
And the changes induced by the sound color options aren't super pronounced, either (see
here). At best, they seem influence things at around -60 dB. I say "seem", because SMSL isn't very clear about their effect in each DAC.
Hear for yourself if you can detect distortions in a signal at -60 dB - I don't. It is also relevant to keep your typical SPL during listening sessions in mind. In a quiet room with around 30 dB of environmental noise, you would have to be listening at >90 dB to be able to detect anything at all at such low levels (90 dB - 60 dB =30 dB). That's not absurdly loud, but certainly elevated.
What you seem to be looking for is something that actually, audibly changes the sound of your system. The easiest thing to change would be to add an EQ. If you want "warmer" sound, try reducing the treble levels. You could also add something like a tube pre-amp with (lots of) distortion. Distortion can also make a system sound "warmer" - but that's certainly subjective and also depends on how the tube is integrated into the design of the pre-amp.