Yes. Just put the left preamp out and right preamp out of your Yamaha into the left and right connections of your REL. And set the left/right speakers to large as recommended. Y adapters would be necessary only if a) you had a separate power amp or b) you only had a mono input on your sub, and had no way to get a mono output from your receiver. But as far as I can tell from your description, neither of these apply in your case.
BTW, they'll start sounding a lot better after you've played them for a couple of weeks, Maggies sound kind of constipated until they've broken in. I wouldn't spend too much time on sub adjustment until they've burned in since low-frequency extension will increase. Just rough it in for now so you can enjoy them.
BTW, they'll start sounding a lot better after you've played them for a couple of weeks, Maggies sound kind of constipated until they've broken in. I wouldn't spend too much time on sub adjustment until they've burned in since low-frequency extension will increase. Just rough it in for now so you can enjoy them.