berghs.kedjan: If you want to make a recording with piano and song Im thinking that you are going for an acoustic sound and I sincerely think that combining 2 different piano sounds is not gonna make your life easier.
A good way to start could be to turn the limiter and the reverb off in Pianoteq, then get yourself a decent vst/rtas reverb, (whatever keeps your boat floating), then mix the song using the same reverb for the vocal parts and the piano (although they could bleed different amounts into the reverb according to taste and style and the sound you want to accomplish).
I dont think the C3 sounds "artificial", I think it sounds like a concert steinway. They tend to have less imperfections and give a more neutral tone then say a malmsjö grand, yamaha grand, or uprights. I would consider though that you use the K1 for a vocal/piano mix, but maybe thats just my taste. I mainly use the C3 for playing classical, usually modern classical.
The pleyel is very nice indeed, it has those small "imperfections" or how to put it ? that makes it special. Consider though that the c3 resembles that slick and less imperfect sound that you get when playing many steinway grands.
The reverb plays deep importance, and the spatial image of the recording. What kind of room do you want it to sounds like, were is the piano and vocalist positioned in the room and soforth.
Recording is sometimes fast, but mixing and mastering music usually takes much much more time and effort.
Im babbling now, well anyways, hope Ive said something meaningful. Good luck !
