Most satisfying system change in 2017?

DIY US cleaner
K&K Audio Trio phono preamplifier
New found replacement tubes for above
Minor speaker adjustments

I upgraded my HT by replacing Klipsch KG 4.2's mains with Klipsch Rf-7's. I also found 3 RC-7's for center and surrounds. And I replaced my dated Onkyo with a Denon Avr-x4300, and a basic Sony bluray with the UDP800.

Everything blends nicely sonically and the sound is the best I've owned. And, even though my 65 inch Samsung is only 1080p, the picture has improved with the 4k upscaling and with 4k discs too. It seems the higher resolution provided by the 4k disc allows my tv to live up to its maximum potential. Next year I will buy a Sony or Samsung 70ish inch with 4k and HDR. I'll have time to acquire a collection of 4k blurays.

Nice thread @knownothing!  Thanks for starting...

2017 brought in quite a few major changes in my system, like some others here, and I can narrow it down to my most significant changes..... 1st, going back to 300b based SET amplification (Coincident Frank mkIIs), secondly, adding an amazing and fantastic sounding preamp to the mix (the Backert Rhumba 1.2), and finally cabling that tied it all together (Cerious Tech Graphene Extreme speaker and power cables, Teo and HFC ICs).

2018 will be a year of “enjoying and discovering more music”. Not that previous years weren’t, but I don’t anticipate any major changes for the foreseeable future.

Wow, great posts!  What prompted the OP was finally finding the right cartridge for my vintage Thorens TD 150mkII.  I installed just this week an Audio-Techinca AT 150Sa which is an evolution from the AT 150MLX no longer available. Right out of the box clearly better match than other similarly priced cartridges I have tried.  Can now play with B&W digital sub with zero or at least unnoticeable single digit Hz rumble.  45 rpm recordings were especially challenging before, not now.  New AT cartridge has excellent tracking and bass, ruler flat frequency response. According to only review I could find, this cartridge is supposed to have more fully fleshed out midrange compared with the 150MLX but reserving judgement on overall sound till broken in.  Grado in system previously was champ in that department, but rumble was awful.

Doing major upgrades to my Naim system.  I replaced my Naim NAP 250 amp with the NAP 500,  I replaced my Naim CDS-3 CD player with the Naim 555 CD player with 2 power supplies, I replaced my Naim 252 pre-amp with the awesome Naim 552 pre-amp, and I just ordered a pair of Grandinote Mach 36's to replace my classic Linn Isobariks.