Well I've run the GS690, it can play fairly high and depending on the door and angle of the 6x9, opening, it will not beam too badly up to 3k or so. Can you run a large format tweeter? Anything in the 2k something ish range? Like for instance, I'd like to try Stevens' tweets with GS690's. I've run the Stevens tweets with their woofers, and they are just damn awesome.

Have you sweeped the GS690's in their door location to see where they start to lose it? Or are you just wanting a wideband to try?