can I connect 2 sources directly to power amp (one XLR one RCA)

I have done this on a McIntosh MC462, which has a selector switch on the back. It worked. But when I unplugged the XLR cables, volume on the RCAs increased significantly. I’m unsure why?

Hello AudoCanada!  If the power amp has a switch on the back for choosing the input you want to use, it's probably OK to plug in both inputs. If there is no input switch, don't do it! The inputs will be wired in parallel and they will interfere with eacj other. NEVER flip input switchs with the power on! You are risking serious speaker damage, and possible amp damage.. Happy Listening.

Only when there’s a  seperate input  switch. Listen to , what’s the best option ! 

Hello,

Buy the Lumin P1. It has analog inputs so you can plug the Node into the Lumin. The Lumin P1 also has several HDMI connections. Since the P1 is a DAC you can run the NODE into the P1 using a coax audio cable. The other way is to get a used preamp for a few hundred dollars. 

Even if it has an input switch, those switches are generally not designed to be used as an alternative to a preamp and may not be the most suited to frequent switching back and forth. Even if feasible, it's very sub optimal as a long term solution to input selection.