are the headphone/output usable for connecting to a mixer/monitors or are they noisy or unstable?
I'm probably the last person to ask about this. This is the first digital keyboard I've ever owned. I've played on a few digitals through the years, but I've never hooked one up to a mixer or anything but other people's sound systems.
I just now tried listening through the little $20 headphones you get with the survival pack. I didn't notice anything I'd call noise noise or distortion. I did hear some very subtle differences. For instance, I can't hear any difference between piano1 and piano2, with the headphones. Through the speakers, I can hear a little more reverb with piano2. Also, the harp sounds better with the headphones than through the speakers.
This may all relate to the master EQ settings. I haven't tried fooling around with that yet. All in all, I'm pretty pleased with the headphones. I thought for sure I'd have to buy a better set, but maybe not.
The violin is still bad through the headphones though. The violin sound is just terminally bad. String ensemble is OK, though.
i'm thinking about using it to record songs. how are the drum sets
I'm not competent to judge. Snare sounds like a snare, I guess. Timpani... church bells... the few things I've tried all sound good to me. But again, I've never used the drum sets on any other keyboards.
Take that back -- I used the drum roll for Miss Hometown pageant once. Sounded like a drum roll to me.