I think I am just going to buy a couple of 12" Matala rubber disks and go with them. It won't cost that much money, likely do a better job and be less of a headache to set up. Also, I won't have to worry about purchasing and figuring out how to employ separate check valves.
My Matala disks work great! They've been in there a year now, and there is not any increase in backpressure, so I'm thinking they don't need cleaning yet.
Beware buying Matalas from eBay. The sellers buy a Matala kit, take the disk out, and then sell the base only for the kit price (free shipping!), but disguise the fact in their slick ads that they took the disk out. They show the original box in the ad that shows it includes the disk, and show a picture with the disk, but state in the fine print it's the base only. I paid a normal price for what I thought was the whole kit, but then ended up needing to order the disk alone!! Buy from a reputable pond shop or Matala.