I use an SPL headphone amp that does some unusual stuff that lets you sort of construct a speaker-like sound on cans. It's a great headphone amp even without that feature, but it does do some interesting and useful things when using it.
It has so much more dynamic range and detail than the headphone amps that come on gear that now I can't stand listening to cans without it, even when I don't use the blending feature.
My open back cans are Audeze LCD-Xs; they're very good headphones. Kind of a bargain, given their level of detail and transparency. I generally track with closed-back Beyer DT-1770, or DT-770 (they're sonically different, so I use them for different things).
Even the DT-770s benefit from a great headphone amp. I wouldn't have believed how good they could sound until I got the SPL. I have some Sennheisers and others around here, but I like what I like.