What iems are you using now that require external amp stacking? And what is your current dap that can't handle iems? Based on my lastest dozen of dap reviews and a ton of iems, i only found the need for a portable amp if i want to change the coloring of the built in headamp or to "clean up" the coloring with something more transparent. Full size demanding headphones is a different story, though
Sorry guys, i don't have P1 for comparison, but based on reading people's impressions of P1 and spending a few days with my P2 review unit, this will be an upgrade in sound sig for many people. I was listening and comparing last night P2 vs LPG, using W900 and Zeus XRA (both with 1960 balanced cables) and sound sig is very close, with the only difference LPG having a little better layering, but not by mile.
Second knob really makes it stand out as something totally different, but as i stated in my initial impression, i only found it practical for my personal use when assigned to a volume control where it adjusts the level in 2clicks at a time - very useful when going between headphones with different sensitivity and need to change volume faster. Btw, knobs are not tight, so you can turn them easier. 2nd knob is just a bonus, not a necessity, but it makes it look cool and gives you extra control. Actually, i also enjoyed assigning it to fast forward/scrub through the track, really fun way to get to the exact position in the track. Assigning to a filter is probably not for everyday use, but very helpful for testing. I need to spend more time with filters, but this is the first time i hear a more noticeable change, with other daps it's too subtle.
Also, balanced output is not a gimmick, you get higher power and improvement in soundstage expansion.