Hey dude this was covered early on that the stock pad's sound more aggressive in the upper mid - lower trebles region.
The solution for those sensitive to this was purchasing the Focus A Pads. .
Ha, Must have been fun modded though
Dude! you need to do the grill mod even if it's out of curiosity to see how much higher the he560 can go.
It's basically a given that Hifiman planars benefit from the grill mod.
I personally don't think you could hold out with your modding skills lol
I would say $200 is not going to get you excellent sound but if you like any amp that fit that criteria then great and be happy what's in store for you once you go up the ladder in amps..
Also I have the O2 still, and it's a bit harsh when pushed but any small amp just not doing justice to this excellent headphone.
The he560 sounds great on anything but also its transparency makes any improvement noticable so it will keep climbing with your system. . .
That being said,
I would not settle for an Emotiva mini.. I herd that with an AlphaDog & a lcd3.
Was not impressed. .
I would skip most mid tier(schiit) that makes you waste more money on upgrades like tubes, and try to get better.
I can only recommend what I know for shure and herd sounds musical:
My recommendations:
Oppo HA-1 amp/dac combo.
Bottlehead SEX tube amp.
The Virtue amp on speaker tap.
Most Audio-gd stuff.
For minimum basic nice amp on a budget, I would get a $100 schiit vali but don't expect miracles because we can't overlook that the he560 is still a planar and loves power.