Hm.
Well, if it doesn't cut if for you, you can use the preouts on the Marantz in order to use your HK's amp?
Hm.
Dunno man.
Does the multiroom flexibility able to play the source at the same time to both outdoor/indoor? Is this the main reason why you just can't pick up a new stereo receiver for $100? It's most likely because you want the sources connected to the Family room system used for the outdoor? If you look at any of those particular sources you want, do any of them have more than one set of output jacks?
Just throwing out ideas in the case you might be lucky enough to spend even less, and keep your good amp as you say.