Most satisfying system change in 2017?

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. 

@inna 

ill try those out. Should be able to source those via Craigslist easy enough. 

For me "roon"
It's Sooloos Meridian without the price tag, but better--the generation for high end

Here is a review.
https://www.google.com/amp/s/www.techhive.com/article/2923915/home-audio/roon-is-must-have-software-...

Built speakers, TMW config.  Crossovers are modified from Icon Parsecs. Drivers from Seas, ScanSpeak and Audax.  Stunned at the results.  IMHO they compete with factory towers @$10k. 
(Unavoidable pride/bias I suppose, but verrry gratifying project). 
Timbre and detail..can’t get any work done cause I can’t walk away.