I've sold all audio gear due to significant life changes. Ive moved to a headphone only situation and placed the majority of my music collection on digital cards in Onkyo DP-X1. Own grado 225e headphones, various iems of reasonable price that i can drive through the balanced output. Just purchased a pair of sennheiser massdrop 58xx headphones and a balanced cable. I suspect the DP-X1 will drive the senn's. However, was wondering if an external portable amp is the way to go. I'm looking for recommendation for affordable portable amps to drive higher impedance/lower sensitivity phones using the DP-X1 if I decide I need to extract more from the senns. If I see this correctly I would be connecting the 3.5mm headphone out to the line in on any portable amp making the need for a DAC/amp combo a waste of $$ at this juncture. At the time I bought the DP-X1 I didn't foresee the lifestyle change and plan for more flexibility with the DAP. I like the sound of the DP-X1. Thanks in advance.