....
Currently, the SBx is failing more and more.
My requirements:
- more responsive and quicker launch than SB
I think your Synology may be the weak link here. Which model is it? Many used Atom processors that simply don't have CPU power these days. I run LMS on my i7 powered home server, and it is super responsive. It is also very responive on a humble, 15 year old Lenovo Thinkpad X series running Ubuntu in my weekend cabin.
- being able to control from a laptop and mobile
The SB is super easy to control via web interface, go to LMS' IP address and add :9000
There are also apps for smartphones and tablets, Android and iOS. I use Squeezer on Android.
- being able to display cover art on a tablet or so would be a very nice plus.
See above.
- preferable DAC quality comparable to the Eversolo DMP A6.
I just use the SB Touch as a front end to a DAC via coax digital. The DAC supposedly was pretty good, but hey, that was a while ago.
- either LMS support or alternatively being able to build complex playlists (cfr. iTunes)
itunes? Ouch... :-D
I still haven't found anything that is as flexible and adaptable as the Squeezebox ecosystem, and it's been nearly 20 years.
I also used to run LMS on a Synology server for a while, but it's the Synology I kicked to the curb. Most come with underpowered CPUs that age quickly, which results in unacceptable performance for more complex apps running on them. They do well with basic storage protocols, but for anything that needs a reponsive UI they age quickly. I could see myself using one as a RAID storage unit, but with online sotrage being so cheap and very fast internet, I prefer to protect my music collection online rather than on a RAID drive at home. These days I just buy a new, high capacity drive rated high for reliability every other year, and run a script to keep a local backup. Currently my main drive is 8TB, and the "backup" (which I use for several devices) is 12TB.