Metaxas Solitaire ll Amp

volume  seems less on right side , than left. output recapped, etc. a few years ago . Any ideas ?

system :
Metaxas Solitaire ll power amp
Audio Research LS17 SE preamp [ less than a year old]
Audio Research Reference CD-7 with upgrades [ less than a year ago]
Luxman PD-121 with black widow arm,Turntable
Cary Audio , phono preamp
Verastarr Grand Illusion Pwr cables and interconnects
Focal Utopia Diablo   speakers 
Switched IC`s from Preamp : No Change in balance volume , Switched speaker cabling : which also switched  higher volume to opposite speaker .
   Leads me to believe  it is in the Amplifier ????  Thoughts on this ?
Thank you for your  quick and insightful response.
  Switching  IC`s from ARC LS 17 SE at the amp made no discernable difference .
   Sad but true I am a plug - n - play enjoyer ,  concrete  cowboy kinda audiophile [ got the hat , boots and truck - No Clue !] .   

   Kind regards
Also check out this page for more info on your amp:
This passage seems possibly relevant:

3. OUTPUT TRANSISTOR BIASING: The SOLITAIRE has 4 pairs of output transistors and when 'biasing' the amplifier it is wise to check the biasing of ALL the output transistors to ensure that one or more of the devices are not conducting more current than the others. This is especially important when replacing a power transistor. Also check the different biasing currents between the NPN and PNP devices. If there is a large discrepancy, replace the 'driver transistor' (also mounted to the heat sink).

When did you start having this issue? Have you definitely isolated it to your amp? Seems somewhat more likely perhaps a tube failing in your preamp despite it being relatively new. Try just reversing the connections between you preamp and amp and see if the volume issue switches channels. Good luck!