I have the Ares II, not the Terminator. I concur, if using OS, I use the ‘slow’ filter vs ‘sharp’. ‘Sharp’ is just too ‘digital sounding’ for me. But following the latest firmware updates, I actually prefer NOS mode, which does not use the filters at all. I feel overall that provides a more analog sound, and as primarily a vinyl guy, I have come to prefer the NOS mode.
Play around with it, you won’t break it, and over time, figure out which you like best. And it could be that certain recordings like one over another.
Great DAC, enjoy.