Balance knob ..

So I'd say I've been a budget audiophile for 40+ years. Used to sell audio at Audio Warehouse in Cincinnati in the '80s. Currently I have a pretty big room with 12' ceilings, but different open areas behind each of the Maggie 1.7is and the Emotiva BASX 10" subs behind each. All driven by an Emotiva XPA-2 Gen3 and old CJ PV-10AL preamp. Listening mostly through a Bluesound Node 2i. CD player is a Panasonic Aventage BD1060 disc player. I have the sound, honestly, pretty damn great. But I am realizing a bit of bias to the left speaker. I think this is because that speaker has a lot space behind and to the side whilst the right has less and more complicated space behind and a closer side wall. 

I have always been told - and believed - that you shouldn't ever mess with the balance knob. But if the sound is a bit UNbalanced isn't that what it's for? Just to "balance" the output? But then I think with more signal going to the channel that the knob is turned to - which will screw-up imaging, soundstage, depth, etc., no? 

I am kinda stuck cuz I can't move the speakers or have a dedicated listening room. 

milostyn, Actually I agree with your analysis.  If I had a balance control on a remote I'd use it to correct recording imbalances. But for system set up I used the XLO disc which has an 'out of phase'  section so my system is fairly well dialed in and I do not have (so I cannot use) a balance control. When I last had one (in an old SP10 I rarely used it because the effort of dialing in a disc without a remote control was not really worth the effort - too fussy for me I think.

FWIW, I think OP's pre-amp does not have a balance control.  I really didn't think the small change OP might incur by buying a new pre-amp would be worth the expense, nor was I sure, with his room, that out of phase information on a disc would be all that important. 
newbee, I think you are right. The CJ does not have a balance control.
Incorrect phasing is always important if you want a solid image as well as the right volume for the location of the image. 
In thinking about it it is hard to describe the effect when you drop the volume on one side 1 db while at the listening position. The louder channel takes on more weight I suppose. The image is crooked? The image is blurred to the louder channel? Certainly the instruments located on the quieter side lose some of their presence and gain some on the louder side. Instruments and voices in the center lose some of their definition. 
No you're both wrong, CJ PV10AL DOES have one. Why would I have asked the question if it wasn't available to me? 

Phasing I have some understanding of. I have Stereophile test disc. What is an XLO disc?

I cannot afford, esp since it has a balance control, and would not risk replacing the CJ.  I have loved it for 20yrs and would have to spend a fortune (to me) to replace it. 
Just use that balance control. it will correct your problem. That is what it was made for. Personally, I would be reluctant to buy a amp without a balance control. Especially true for tube amps. If you get paranoid enough about this issue, you can convince yourself of all sorts of problems. Take a deep breath, try it, and listen. Don't like the results? THEN try something else.