ATC or Audio Note (2-way)

Very different? I've heard ATC but not AN. (I've used a lot of AN components in various DIY, though).

Thought both were very mid-centric?

I’ve heard both. It doesn’t seem likely you’ll get much more resolution by tinkering with the ATC and you’ll possibly compromise its sonic balance (btw most ATCs bar the big ones are bass-shy). Modding the AN will probably modify its sound -- but do you really want that? These are not exactly cheapo speakers.

I would suggest another diy challenge: purchase vintage japanese speakers and mod them to approach contemporary performance standards!

I've owned both

ATC SCM11v2s

Audio Note AN-K SPx/SPe

Two very different price points.  The ATCs are very resolving, fast transient response, can play really loud and still maintain tonal balance and soundstage w/o compression.  They do need power to wake them up - so low level listening was their weak point, imo.

GR Research did a video on these for mods - their freq response is down a bit on top (I would agree), the mod evens this out.

AN-K's are much more efficient - best way to describe the sound is natural, relaxed and tonally 'right'.  Just as resolving as the ATCs, but they play better at low to mid-high volumes.  They don't do as well loud, imo.  I've not seen any measurements on the AN-Ks, so can't comment on mods.

ymmv

Thought both were very mid-centric?

no

ATC's are not midrange centric, they are not "smiley curve" sounding as so many speakers are.  Smiley curves sell MUCH better than flat speakers so they are vastly more popular.  Manufacturers know this as most are not in the business to build the best speaker, but to sell the best selling speaker.  If you like music, bass boosted smiley curve actually reduces resolution by elevating bass unrealistically compared to "heart" of the music: voice, piano, violin, guitar.  The midrange now sounds reduced, pushed in back, not like the band or orchestra or instrument really sounds.   This is why many in the high end "accurate" camp use piano for demo.  Its easy to hear changes to EQ on piano.