Unsurprisingly in retrospect, the issues I was getting - sibilant treble and "deconstructed" bass - supposedly with specific tips, was fit-related. With the New Bee Large Memory Foam eartips (search amazon for "new bee ear tips" [I don't like to link to stores on here], it is the 6 pairs, 2 pairs of each size, item priced at $6.99 currently), and the default balanced filter, the tuning of the FH7 is just about perfect to me. The only "complaint" would be that vocals sometimes seem a bit recessed, but if that is due to having a dip ~500Hz, that's what I want (extra clarity), anyway. The seal and comfort with the New Bee tips is also just about perfect - no comfort issues at all anymore. Finally, no hiss is audible at the volume levels which I listen.
The FH7 is my go-to headphone for every use case (awesome for video games, even, especially if using virtual surround). Near-perfection (for my tastes and ears) at just $450. If I buy another IEM, it will be another FH7, for fear that one day my current FH7 will stop working.
I have decided against getting an RME ADI-2 DAC FS. Would be a waste of money over something like a Topping D50S (which is probably what I'll get) since I don't need the ADI-2's extra (mostly EQ-related, which I have Equalizer APO for [absolutely no need to EQ the FH7, though!]) features. Further, a very small, if not imaginary (outside of inaudible measurable improvements), difference in sound quality is not worth $900 to me.