Impedance Question?

Quick and dirty answer: you want the amp to have an input impedance at least 10x the output impedance of the pre. 

Here's a solid thread: https://forum.audiogon.com/discussions/how-to-match-preamp-and-power-amp

It is so confusing isn't it?! I'm currently looking at room measurement mics so I can stop going completely by 'feel'.

Good luck! I use a dared mc7-p preamp (class a tube) with my class d monos and it sounds beautiful. I think it only has an output impedance of 100 ohms and there is certainly no roll off in the bass zone.

Well, I'd say you should trust the manufacturers more than us. But putting together what they both said, I'd say they seem like they'd work. Proof is in listening, of course

That said, I have a Dared MC7P (there’s a dash in there somewhere..) and it played nicely with a Crown amp that had in input impedance of 10k and currently plays well with ICEpower monoblocks. The Dared apparently has a low input impedance.

It’s all so freaking variable!

@georgehifi oh man, sorry. I didn't mean to repeat myself. I've the schematics for my pre somewhere, I'll see if I can figure out what value the coupling cap is. 
What formulae are you using to calculate low frequency roll off?

Wait, the answer is a number (I've yet to calculate). Is that the gain or the frequency? How do you find the other?

I think larger value caps are too large..