Unbalanced Mono plug is TS. Unbalanced Stereo plug is TRS. TS to XLR is fine if your keys have unbalanced mono 1/4" line outs and your powered speakers accept balanced or unbalanced XLR ins. Make sure you get the gender right on the XLRs though. They tend to come in both female and male connections.
One other thing. TRS mono is usually a balanced output/input. This will also work if your amp has balanced inputs and your keys have balanced outputs.
Anyway, upshot is no problem connecting directly to powered monitors, powered computer speakers or even a quality home theater or stereo system.
Line levels are all compatible and frequency response should be adequate.
Even so, a small mixer is always a handy thing to have.
Just make sure all the plugs fit properly and you're good to go.
Gary