Why not a used Loki Mini? There is also the Fosi Audio P1 which probably fits your needs best right now from what you described. Also, the Bellari Audio EQ570.
I agree with @AnjTheAudiophile I have the Loki mini and love it and use it for primarily the same purpose…to give my DT880/600 a bit of bass and low mid boost. It also adds some sense of depth to the soundstage. Also handy for bringing forward those vocals which need a kick. (All this is if your budget allows at this time, of course.)
some people also just don’t like software eq (I’ve never had a good experience with it lots of bugs/issues and a general hassle compared to just turning a knob)
I also do not know if this is placebo or not, but I feel that hardware EQ works better. I feel as though there is a slight improvement over using something like Peace. I found the differences more pronounced when the EQ is built into the actual dac as is the case with my Monolith 788. I have heard some people say the same about the RME ADI-2 dac. Again, I haven’t done extensive testing, so it could just be placebo.