Weak link

is there a vaccine for upgradeitis?  I can't imagine your system not sounding fantastic but yeah I understand the disease "What am I missing???"  There is no cure but there is always ways to stave off the impulse to mortgage the kids and provide temporary relief. 

Cleaning all the contacts could be all it needs to get that last ounce of nirvana.

Moving your speakers is also great pastime (don't forget the blue tape to  return them back).  I'd also try moving your sub to different places in the room, closer to the wall or pulled out more into the room,  away / closer from the corner .   As you've become attuned to the way your system sounds that original setup might not be optimal anymore.

If you really need to spend money a couple of acoustic panels leaned up against the wall at reflection points would give you some ideas what treatments could do and if like what they do.

The last option if all else fails is for me would be to add an additional sub (or two)  to address the inevitable dead spots in the room.

It's the journey... remember it's not the destination but the journey

Deep333- I’ve used subs on and off for 30 years. Used rel subs on and off for over 20+ years. The most benefit I got is in a small room (12 x 11) and in very large rooms (27 x 16’).

And of course HT in a theater room. The best systems I’ve had didn’t use subs and the best audio setups that I have heard didn’t use subs either.

I agree that you can use subs to treat certain areas but I’d rather use a speaker that fits the room that gives me the bass quality hat I’m after without subs. I have subs just sitting there not doing anything and I’m fine with that

The only thing that needs upgrading if you want to go all the way is the Dac and streamer…I would get the Playback Designs MPD-8 and their streamer too…

I know it's been said over and over but I'll pile on for room treatments if possible.  Best bang for the buck IMO.  Just putting panels at the first reflection points is pretty much a game changer.  At least it was for me.  Very cost effective DIY panels or just hang some thick blankets to try it out.

Let us know.        

Room acoustic treatment and dedicated lines. I would re-evaluate after the room is done.