I have SP1000cu and I was looking for a more portable DAP.
Was comparing SP1000m, SA700 and SR15.
To be honest, before visiting the shop, my mind was set on the SA700. I don't think much of the SR15 at all, except I knew it was the cheapest.
I found that with my 64 Audio N8 CIEM & EA Lionheart running 2.5mm balanced, the SR15's sound signature is surprisingly similar to the SP1000cu. The SA700 sounds different with a more forward vocal than SP1000cu, SP1000m and SR15.
I have also compared other brands' compact DAPs, but nothing come close to the SR15 in terms of size, SQ, smooth UI & user experience, lack of annoying hisses/popping noises, aesthetic design and build quality. Don't discount the SR15 (like I initially did) just because it is an entry level AK DAP, I can see AK has put in lots of efforts in the development and sound tuning of SR15 and IMO, it absolutely hits the sweet spot in terms of price, SQ and portability while many other manufacturers failed. To me, the SR15 is a landmark product from AK.
In the end, I got a SR15 and really enjoying it a lot. Out on the road or in any less than ideal listening environment, using my CIEM and streaming Tidal (mix of HiFi and Master quality), I don't feel that I missed out anything (SQ-wise) as compare to the SP1000cu.
I still keep the SP1000cu for quiet evening listening though.
Oh, one more thing, out of all AK current DAPs, I think the SR15 (and probably the SA700) deserves to be use "naked" without any leather cases (which are usually quite thick and they hide the brilliant tilted screen design elements). Just hold the bare SR15 in your palm, feel all the edges and the contrasting feeling between the aluminium body and smooth back plate, admiring the perfectly executed industrial design and complex geometry of the machine from various angles while listening to your favourite tunes is quite an enjoyment.
I really wish AK can keep developing the SR15 while retaining its form factor/design, or perhaps bring us some meaningful special editions with heavier case materials (brushed SS, CU or brass?) and higher native DSD support etc.