To answer one of my earlier questions I went ahead and bought those Shure SRH840 studio monitors. I needed a closed back can because silicon tipped IEMs were giving me swimmer's ear, and I find these Shures to be pretty nice. They have the isolating quality I was looking for, and they are actually quite comfortable, once your neck muscles get used to the added 317 grams on your head! Yes, they are huge, and you won't win any cool points while wearing them.
I did an A/B test with the Audioengine D1 and C&C BH. The BH was fed with the RCA out of the D1 with volume pot fully clockwise. The headphone output stage of the D1 was far warmer and with a less impactful bass than the BH, even without the LF switch on. There is no question this is a great pairing. I have maybe 50 hours on the Shures and they seem to still be evolving, or my ears are. The muddy bass I felt they had out of the box has been replaced with a sharper, impactful bass. The treble has been tamed somewhat as well, but becomes fuller with the BH driving the proceedings. They are more detailed than say, the Senn HD280 Pro, but nowhere near as aggressive as the Grado SR325is, which is my go-to on ear can. I have to say that I prefer this setup to the Klipsch X10s. Should sate my desire to upgrade the amp for a bit, but we all know that won't last.
For now...I love this amp. I love this setup. Joe Bob says, check it out.