Ok so there's a program out there that makes the best wavetables I've ever known. It's a downloadable program that makes really ridiculous FM wavetables, and it makes them specifically so that they can be imported into Serum. Here's the link:
Once you've downloaded it, set it up, and have made and exported a sound, you can import it into Serum using the "import constant framesize (pitch avg)" option. Sometimes that doesn't work though, so in those situations, you want to open up the oscillator edit menu, type "2048" into the formula parser (without the comma), and then drag the exported sound into the frame (while the oscillator edit menu is still open).
EDIT: Using the formula parser "2048" method also reduces lag, just in case that's something you'd need to know.
EDIT (again): Guess who's an idiot? ME. You can import it by just dragging the file into the box in the bottom-right that says "FFT 2048." *bangs head on wall*
Sounds like a ton of work, but trust me, it REALLY pays off. You want to know where Virtual Riot got his "dying" wavetables in his second preset pack? >:D
Also - this is the important thing - I'm on a trip that's going to last till the end of October, so not a whole lot is going to be happening here on NG for me, sadly. But, I'm obviously not giving up electronic music in the slightest, and I'm sure that I'll be working at 110% capacity as soon as I get access to my home setup, to which a huge Yamaha P60 keyboard was added days before I wasn't going to be able to use it for over a month. :P