Thank you for the replies, and some great ideas. The point of running setup again should have been obvious, and probably would have if I'd had a monitor connected to see the Denon on-screen menu. As it was, we moved into a new house nearly a year ago, and before the HT was unpacked, basement flooded, inspiring many months of work on my part. During that time, purchased the Source speakers and they sat in storage (after a quick connection to be sure they worked). Now the Denon is out of moth balls, but still no monitor connected. Rerunning Audyssey should be the next step, if previous settings are still in effect, the mains are probably set to "small speaker". Also, I was reading in the manual of AVR-X6500H, that impedance is selectable in the menu too, and this is probably true for my X3000 as well.
Also appreciated the idea of using pre-outs to another more capable amp for the Source speakers. This would be a great option, especially if Source's might be upgraded later to larger electrostats. I am fond of their qualities.
Taking it to the next level with Denon's sister Marantz is another good idea. Although, not sure I'm that much of a hobbyist. It opens up another level of upgrade potentials that seem endless. I was looking at Emotiva amps (really like the modular construction), and thinking that might work, then noticed the price of the matching preamp, and thought oops - this game is for enthusiasts with a different budget for such endeavors.