Pi based streamer expectations on sound quality

I use an Arcam Movie 5.1 as a preamp/cd player into some Linn Room Amps, biamped, and biwired into some Monitor Audio Monitor 3 speakers that I've recapped and rewired, stuffed etc etc, and for what is pennies in HiFi world, I have what to me seems like a very good system, certainly the best I;ve ever owned, but TBH I haven't auditioned anything in a proper HiFi shop for a long long time. Anyway, liking the sound that the setup creates using a CD, I began to wonder what a streamer would sound like - CDs take up a lot of room (!) - so I bought a second hand RPi 5, and a Digi+ Pro (clone?) off Amazon. I didn't expect much, and was fully expecting to have to send it all back, but for a source that I've put no effort whatsoever into making sound good, it's to my ears almost exactly the same as using the CD - damn !!

So, the next stage up would appear to be £120 ish for an IanCanada Transport Digi HAT - but just how much better would anyone say the sound would be, if at all ?