grisly I have owned the i5,now own the 240i & have demo’d the 340i several times with Harbeth M40.1,M30.1 & Dynaudio Excite X18 speakers..
IMO the i5 was the Pinnacle of their lower priced units..It’s build quality was a step up compared to more plastic in the current options..The sound to me was just a bit sweeter,NOT a huge amount but just a touch,like moving from current production EL34 tubes to some NOS Wing C’s if you can relate to that analogy..
I haven’t heard the 250i or the Ace but I can’t see there being ANY difference between the 240i & Ace as they are the EXACT same except for the Ace having the Streamer built in...When I demo’d the 340i with the M30.1’s & Excite X18’s I found almost no difference between the sound of the 240i & 340i...Changing the the huge M40.1’s made a big difference between the 240i & 340i,those big cabinets & woofers really needed the extra power,solidifying the bass & opening up the imaging & staging...
Currently I own the 240i driving Harbeth M30.2Xd’s & feel it’s about as good as I can possibly get from a Solid State system..The staging could be a touch deeper but I don’t think that’s possible without switching back to a tube set up...