Thanks for the detailed answer.
Sadly I'm not into the IEM stuff because, no matter which one I tried, my ears start heating badly in no more than 30 minutes after I start to wear them.
I am really considering asking the audiologist to mold some inserts specifically to my ears.
Till than, I use 3 cans the DAP, Oppo PM-2 (excellent in quiet environment), Sony Z7 Mk2 - my favourite closed back cans and Sony wh1000 xm3 while on the go. All these cans are low impedance.
What I noticed is that Bluetooth on my x7 mk 2 is subpar to put it mildly.
Do you have any experience with wireless cans on the m11?
PS
Someone offered me a very good deal on a Astell & Kern AS700 but initial reviews are not very enthusiastic about it.
I've a set of Sony Sony WF-1000XM3 which pair beautifully with Sony's NW-ZX300, not so well with the M11 Pro, although I think that's a little intentional on Sony's behalf. It's not that they sound bad just better Sony to Sony, which makes sense, Sennheiser TWS earbuds sound good on the M11 Pro.
Only cans I have are BOSE QC35 II for the jet and now just films as the Sony WF-1000XM3 has pretty decent ANC. As
BOSE has now borked the firmware on the QC35's, I'll likely switch to Sennheiser next time I'm in the market for over ear with ANC, as BOSE's attitude stinks. Also had a set of their Soundsport Free TWS earbuds fail for yet again another common reason. Too much brand arrogance methinks...
Looked at Astell & Kern, however think is vastly overpriced and has a specific sound signature. Not bad gear by any means, equally one is definitely paying a premium for the brand & design. FiiO I feel that your paying for what you get, although yet to see the M15, M11 Pro I feel is fair given the THX amps etc.
Might swap out my black M11 Pro for a stainless steel one and or have a good look at the new M15. On the go I prefer smaller DAP's such as the Sony NW-ZX300. Recently picked up an Acmee MF01, which has some limitations, however for the price sounds outstanding. As long as your ok with a slightly raw & warm sound signature, and for something that only cost $80 it can outperform some higher priced DAP's. I also kind of like it's just an old school player, no touch screen or album art to deal with just a focus on quality audio.
These guys are on the money as sounds great for the price and at times just one simply doesn't want to carry an expensive DAP about. The Acmee with the right cans or IEM's lights up, presenting an almost tube like smooth warm sound signature thx to the MUSES02. This DAP is fun and engaging with few frills and a couple of caveats - Currently Kobra and the Lotus - Black Velvet - is simply

Punch the volume with Fleetwood Mac - The Chain, you be gone, lost in the music, Supertramp's Dreamer kills it, DJ Shadow's Mountain Will Fall, add in Dunu DK 3001 Pro IEM's and you'll be feeling the sub bass...
Ghost - "He is" a must listen, builds & builds ?
Q-6