the mic/line button will select between mic and line level. most of the time, it doesn't select the actual physical connection to be used, but it just might. i haven't read the manual. so you should be able to use the XLR connection, select line, and have the right amount of signal. however, be prepared that selecting line selects only the 1/4" input. in that case, it doesn't hurt to just
generally speaking, you can use the XLR connections and adjust the gain settings on the interface/mixer so that you aren't clipping the inputs. so the actual gain settings on the interface are completely dependent on how much signal is being sent from your axe fx.
i usually start at 12:00 on the axe output knobs, then see how much input registers on the next device, mixer, interface, whatever.
if the interface gain is all the way down and it's clipping, i reduce the volume on the axe.
if the interface gain is all the way up and it's not enough level (not near clipping either), i increase the volume on the axe.
everything else in between is just a balancing act.
Okay I'm a little confused. You said I can use the XLR input on my interface, and switch to line, but then you said it selects the 1/4" input.
Alright, I actually just got off the phone with tech support from Focusrite, and the guy said to switch the interface to Line, which would need me to get an XLR female to TRS male, use the TRS line input on the interface, and then set the gain on the interface to about 4 1/2. Then control the actual volume of the patch via the axe fx. This would be fine right? Cuz the guy said that even though I'm using XLR to TRS into the interface, that it will still be a balanced signal
And as far as the gain settings on the interface, would I want a high or a low gain? Like on a scale of 1 to 10.
No, I said it MIGHT select the 1/4" input. Some interfaces do, some don't, when you press the mic/line button.
This confirms that it DOES select the 1/4" input when you press the mic/line button.
I wouldn't worry about the balanced connection between the axe and your interface. In most situations, an unbalanced signal will be the same. So just use a regular 1/4" cable from the 1/4" output of the axe output 1 into the 1/4" input of the interface and select Line. If you are getting interference noise or hum, you may need to use a balanced cable, but it's usually not necessary for cable runs under 18 feet.
As for setting the interface gain specifically to 4.5, I guess you could try that first. But balancing input gain is just like I described earlier. Pick a starting point on the axe and go from there.
Maybe 4.5 is the most transparent setting on the focusrite. But don't be afraid to change that if you need to for the right amount of input gain.