Trying to match impedance

Are you sure that 1.2K number is right? I'm going to assume that the number might be 12K ohm. This is still rather low for an input impedence.

I would probably steer clear of preamps that have output impedences greater than about 500 ohm unless it too offers a balanced output, in which case you can stand considerably higher. Most solid state preamps aren't going to present a problem, while valve preamps tend to have higher output impedences...though, not universally in either situation.

Where you might start having compatability problems would be with a valve preamp with an output impedence greater than 1k ohm. Generally, you want an input impedence of at least 10X that of the output impedence of the source feeding it.

To answer your last question, you shouldn't damage anything, but you will have a very pronounced roll-off of the frequency extremes and your speakers will sound a whole lot like their impedence plot. Where the speakers dip in impedence, your amp will struggle to provide current and those frequencies will be attenuated.

I suppose you could damage something in tube gear if you could stand to listen to the combination for very long.

I just noticed I misread your balanced vs se numbers and my comments should be swapped with respect to those. Sorry.

The long and short of it is that almost any preamp would be fine using the unbalanced input of the amp. However, in that the balanced input is in fact 1.2k ohm, you'll need to ensure that your preamp choice in balanced mode is less than a hundred ohms ouput impdedence. That's not all that uncommon in ss designs, but almost unheard of in tube designs.

They're out there and if you buy one that has both balanced outputs and se outputs then the worse case scenario would be that you run your amp from its se inputs.