That is not bi-amping... It will work out just fine. You can use a "Y" adapter if your AVR doesn't accept 2 subs.
To set it up I would hook up one sub... Get it located, and set the level at 75db. Once you have that done I would disconnect the first sub, and hook up the 2nd sub, get it located, and set the level for 75db. Once you have this done you can use the "Y" connector and set the level for both subs running together at 75db with your AVR. :T