Thanks for the info in this and related threads, all (esp. Jokeyman123). I bought a PX-160 recently, and wasn't happy with how my Tascam headphones (which worked fine with my old PX-830) were sounding. I bought a cheap headphone amp, and that helped a ton. FYI, the one I bought was from these guys:
http://www.lucidlaboratories.com/headphone-amplifiers
Very affordable, and also neat how they literally make them in mint / candy tins (I chose Altoids Wintergreen ). Recommended!