Having finished mucking around with my comparisons of UPnP servers, I’d recommend anyone else who has the patience to do the same thing because there are substantial differences on a revealing system and they may well have different preferences depending on their system, room and taste in music.
I’d also recommend giving Asset a good try.
I was all primed to prefer Minim because it can handle the management of classical music better, but I ended up finding some sonic limitations I couldn’t put up with, although it has a beguiling midrange, good timing generally and is deft and airy, it’s also a bit bass light. More importantly, under pressure (and this was the crux for me), its somewhat thin treble can become brittle and it losses track of complex passages, muddling the timing and individual voices/instruments/sections of the orchestra etc. It can also sound a little shut in.
Twonky has in my experience a robust bass and seductively massive soundstage, but can sound a bit coarse in tone and texture, and has less air around instruments and breath/body in voices. It is well-supported, contrary to rumour - I got great and very fast tech support.
Asset, which is what was used for most of my pre-purchase auditioning, doesn’t have any easily-pinpointed outstanding strengths or weaknesses and doesn’t really draw attention to itself in comparisons, but is better balanced overall.
Roon RAAT is closest sonically to Asset but can deliver a slightly lower noise floor, greater detail, texture and dynamics together with tighter timing when implemented on a Core run on a dedicated server that’s stripped to the minimum and running ROCK (I’ve posted in more detail on this in the RAAT vs. UPnP thread in the Streaming section of the site for anyone who’s interested).
When doing comparisons, I’d recommend only running one server at a time. Shut down the others and any other NAS Apps you don’t require (careful how you do this: just one at a time so that if anything stops working, you know what to restart immediately). The less processes that are running, the better it will sound, at least in my experience.