I've done my share of mixing and matching with headphones stuff.
Headphones bought and sold:beyer dt770, dt880, grado sr-225, Audio technica A500, W1000, Sennheiser HD600, Sennheiser HD580.
Amsp built and sold: Cmoy, Meta, Pimeta
Headphone out used: Pioneer cheapo Receiver, Denon AVR-1603, Pioneer Elite A-35R <---still using.
For low impedance cans like grado and audio technica, they might be sensitive to the output impedance, but my cmoy ($40 hack job) made the sr225 sang.
High impedance cans like DT880, HD580/600, My Pioneer Elite A-35R ($120 used) killed the meta (bought at $160), Pimeta ($90 hack job) in turns of any sound attribute.
As long as you have a good source, amp doesn't really do much. If you use a computer as source, save some money for a E-mu 0404 or 1212m, because they will give you an improvement which an amp can never achieve.