Weird problem noticed last several playings...

The system: CJ PV-10AR preamp, Emotiva XPA-2 Gen3 amplifier, Yamaha BD-1060 Disc Player, Bluesound Node 2i streamer, Maggie 17i speakers,  2 Emotiva BasX10 subs. 

Fairly suddenly , over last several listenings - especially with the female background vocals on "California Dreaming" there a lack of detail, a muffled sound, and it sounds like much of the detail, punch and soundstage has disappeared on all sources. 

I am hoping (even though they are only a couple years old) it's one of the CJ tubes but does anyone have any diagnostic ideas (aside from "your system sucks, replace this or that. This is particularly galling as I have been a budget audiophile for 40yrs and the system, when right, sounds amazing and just what I want.) 
CJ says it's definitely the tubes. They say I haven't replaced then since '14, but it seems sooner than that. So regardless, they are sending 2 new tubes I bought. So we'll see if that fixes it. If not I am going to send it to them for full upgrade. 
Because I wanted to see if people thought it was the preamp and what they thought if?t might be, duh. Why ask? 
A follow-up that isn't good: as above, I called Conrad Johnson and they said the tubes were well past their expiration date. So I had to wait a  week for tubes to arrive. I got them in today and, while it sounded better, something still wasn't right. I finally thought of turning the balance knob and, sure enough, when I put it all the way left there was very little output from the Maggie on that side and what output there was was very muffled and constrained. So I switched the preamp outputs and the problem stayed on the left side - which to me tells me it's the speaker, right? Could an interconnect or speaker wire cause that? I should think that would be exceedingly unlikely, no? 
Last thing to check is leave the cables connected at the amp, but swap the speakers they go to.