I use a Focusrite Scarlett at home and take a Focusrite Solo out with me on a gig. The Solo doesn’t have as much volume at the R and L outputs as the Scarlett. I have a couple of questions:
Can you provide some more information? Which exact models from which generation do you use/compare - the Solo is also a Scarlett 
And what is “much volume”? Where do you connect to?
If you’re talking about the 2i2 vs Solo, the 2i2 has slightly higher performance characteristics, which leads to this difference in level.
Solutions to avoid clipping if your Master Volume is already at maximum:
-Add a Gain Control in the Global Rackspace and lower its level when you use the 2i2.
-Or lower the level of the broadcast system (FOH, amp).
If there is still headroom on your Master Volume, do the opposite.
Compare the 2 Focusrite devices to determine the exact gain level to modify.
This is what I do when using different interfaces.
I guess that’s what I was suspecting. Thanks for the suggestions. Cheers.
I have a Scarlett 18i20 and three different RME interfaces. Everything else equal, the Scarlett has more input gain on the instrument, line, and mic ins than my RME’s. With single coil guitar inputs I really have to crank the input gain on the RME’s to get the input where I want it, whereas with the Scarlett I do not.
My RME interfaces are higher quality across the board in every way, so I don’t associate the input and output levels with quality.
If anything, I think it’s a slight peculiarity that the Scarlett juices the gains a little. Probably a marketing choice because louder always sounds better (until you start to clip).
Not to mention that RME comes with TotalMix FW software. I love that it can loop back and I can take snapshots.
A common thing that I do it A/B my Gig Performer output with a reference track on Logic. I purchased their RME ARC USB remote controller, and I can now A/B things with the touch of a button. It also includes a wheel that I can use to control the volume to the mains. I keep it on my keyboard, while the interface sits on the floor with its connections.
Back to Focusrite, I have a Scarlett, and it worked well, but if I left the rig running overnight, it would sometimes crash. With the RME Babyface, it’s been rock solid. When I moved from the Scarlett to the Babyface, things sounded, um, different. Frankly, the music sounded worse. But I think it was because the RME revealed weaknesses in a mix, while the Focusrite covered it up, probably more with jitter than with white noise. The Scarlett is nice and quiet for the price. Excellent value.
Regarding levels, I’d turn the loud one down, rather than turning the quiet one up. 