Already looked at the JBL 305P mkII, reports of quite a lot of hiss...
My guess is, the LSR305 has less hiss than your Laney or the CM30. You're unlikely to hear complaints about a little hiss on those because nobody expects super high quality sound out of that kind of speaker to begin with, they're not designed to be used as monitors. Though I understand you still might prefer something with a different mounting option. So I'm not pushing the JBL, I'm just saying you also should look at reports of a product's shortcomings in a fuller context of who the reviewer was, i.e. what they were using it for, and what ideals or other products they were comparing it to, rather than possibly assuming the comparison is valid compared to something primarily designed for a different user and for a different purpose.
I've never actually heard what studio monitors sound like, and I don't know what they're supposed to sound like, but since there's so much fuss about them, I assume they sound very different from your normal high quality hifi speakers.
I'm not all that demanding... I might be disappointed with the 'quality' sound coming out of decent monitor speakers because it might not be what I expect it to be...Give me a warm and enjoyable kind of sound, like I'm used to hearing, from all kinds of sources.
Yes. it's possible that you'll find monitors disappointing. The main conceptual difference between nearfield monitors and even quality music playback systems is that most stereo speakers derive some extra presence and warmth from the reflections of the sound in your room, whereas nearfield monitors try to minimize the effects of room reflections, which gives you greater accuracy but may seem sterile by comparison. It's similar to the effect of what happens if you take your home stereo speakers that sound great in your living room and move them outside for a party. They don't sound as pleasing. The problem isn't merely that you've put the speakers into a bigger space per se, but that you've eliminated the effects of having things for the sound to bounce off of. More on this below.
where I will be playing now, for the next 12 months, is an open space. It's sort of like a loft and there's not really a lot for the sound to bounce off of. So in that respect, I think that calibrating studio monitors in that kind of environment is going to be nigh-on impossible.
Again, studio monitors have no need to be calibrated any more than any other speaker. It's just that people who buy studio monitors are more likely to
care about getting the very best sound out of them, so they are more likely to
bother taking more steps to optimize their sound, via calibration or room treatments. An LSR305 on a stand with no calibration will still sound more faithful to the source than a CM30 will. And getting back to what I said above about the effect of having things to bounce off of. the real benefit of nearfield monitors in particular is that they are designed to sound best just a few feet from your ears (and away from any walls), and if placed that way, that helps assure you hear more direct than reflected sound, meaning the need for calibration or room treatments is reduced.
Which, just as an academic point, brings me to your room with "not really a lot for the sound to bounce off of." Having nothing to bounce off of is ideal, but probably not what you have. If you clap your hands in the room, do you hear any "reverb" or "echo"? That's the sound bouncing off the surfaces of the room. To hear what it should sound like if there was really nothing to bounce off of, clap your hands outdoors. Calibration and room treatments are primarily about getting rid of the effects of putting speakers in a room with surfaces for the sound to bounce off of. So the problem with a loft-like space isn't that there's nothing to bounce off of, but rather the locations and reflectivity of the bouncing surfaces that are there.
Back to the point, you might be perfectly happy with the CM30... especially in the context of shifting from wanting an
accurate sound ("speakers that will make the MP11SE sound like a real piano") to wanting a
pleasing sound ("I'm not all that demanding...Give me a warm and enjoyable kind of sound, like I'm used to hearing" similar to your Laney). You said you have high quality headphones. If they are indeed high quality, then the difference in the overall sound of the piano between a CM30 and an LSR305 (or similar) will probably be roughly similar in effect to the difference between how the piano sounds in your Laney vs. in your headphones. My guess is that you like the sound in your Laney, but find the piano to sound more authentic in the headphones. But if the Laney quality is good enough, you may be okay with the CM30, whereas if you find yourself wishing the piano sound in the Laney were closer to what you hear in the headphones, you should probably be looking at monitors.