everything affects everything
Hey Roybot- here's my thoughts on this for what it's worth. Every place you play is going to be different, whether studio or stage, and you should get in the habit of tweaking your sound to fit the situation. The size of the space you're playing in is a huge factor, as well as the type of treatment the room has (carpet, type of walls, celing height, furniture, how many people are filling that space, etc, etc)
Even in the studio there are tiny changes going on that will alter your sound from moment to moment. Especially temperature and humidity! Also where you place your amp, whether on the floor or on a stand (or chair), in the center of the room or up against the wall... near the corners, etc. The best thing to do is to find a spot in the room where the amp sounds the best to you, then tweak from there.
Your amp will also sound different depending on how close or far away you are from it and whether it's facing you or not. It's just nature and how your ears interpret things.
When I bought my first tube amp, I spent hours and hours trying to find "my sound." When I finally found what I wanted -- a phat, thick, rich, beefy tone -- I wrote down all the settings so I wouldn't forget them. Then when the band showed up for rehearsal EVERYTHING changed. The amp settings were the same, but all of the other instruments made it pretty muddy and I was drowned out.
So I modified my sound and modified the way I was thinking. Every instrument needs it's own space in the mix INCLUDING it's own EQ space. What might sound fine on it's own OFTEN clashes with other instruments, and you just have to trust what your ears are telling you. Whether we like it or not, guitars often sound better with less bass, more mids and treble, and it will cut through the mix better.
Where is the amp in relation to the other instruments? Can you move the amp on stage to a spot that would better compliment the other instruments? It's all about experimenting, tweaking, and knowing your equipment well enough to coax out the sounds you want to hear.
Hope this info helps. Cheers, Rez