In General, it should be possible to plug in analog outputs of Instruments on any XLR Mic/Line Inputs as long as the gain range of the input is wide enough to get a reasonable signal.
Depending on your situation that may lead to a ground loop generating Hum.
Since practically all manufactorers of Audio gear still don't deliver ungrounded symmetric I/Os (which is technically known as the least problematic way to avoid that Problem since more than 100 years but costs several Cents of Hardware in the Gear) you will have to use a DI Box with a Ground lift Switch then.
Warning: NEVER isolate the protective Conductor of any Gear. That may stop Humming, but it is absolutely life dangerous! DO NOT DO THAT. UNDER ABSOLUTELY NO CIRCUMSTANCES. Use DI-Boxes if necessary!
A DI-Box transforms an unsymmetric grounded Signal into a symmetric one and usually has a "ground lift" Switch to stop Humming by isolating ground levels of both devices from each other (which is the 2nd best Solution for that Problem, also known over 100 Years - 2nd, because it needs additional Hardware and operatig that switches).
Standard DI Boxes will also transform the signal level by a Factor of 1:10 to match line vs mic Input Levels so that will also solve an eventual Gain problem.
Another Solution would be to use optical digital transmission but that is out of Scope here since the StudioLive has no optical Inputs (and while using external converters is sure possible, it will be by far the most expensive solution and makes no sense here).
Especially with E-Guitars you may even need a DI Box with a "High Z" Input to get a reasonable undisturbed Signal. That is a very special requirement then.
