I run my gig setup both ways.

For the duo, I use the Sonar (Roland) VS-100 as my mixer. 2 vocals with FX and compression... keys in stereo... my other vocal processor (Roland VP-7)... digital coax in for a digital out on my CD player if needed. It also has all of our tracks
backed up on the mixer’s SD drive. Main out 1/4” balanced to the powered speakers.

When I do a solo... my mic to the keyboard... balanced 1/4” TRS to XLR male into the powered Speakers. I use the knobs and sliders on the Pa4X to control the balance and overall volume. Works the same way as using a mixer. Plus, the MAXX audio tools help to shape what you want.