Clark's right, Earthlinked might be the best answer for this job. I forget DX options lately due to distributer issues.
J

The crawl walls are ICF. I put 2" XPS on the inside of the footers and 3/4" XPS under a rat slab throughout the entire crawl space area. I will have to play with the distribution more after we finish building and move in, but so far, for working, it's comfortable throughout the whole house. Since Christmas I've been running my pellet stove mostly in order to use up the ton of pellets that came as part of the stove deal. The air handler runs constantly so air is circulating through the whole house. Interestingly, I do have an issue with air movement past the thermostat in the hallway, it's almost nil! The living room gets up to 72+ before the thermostat hits 70 and turns the stove off. And with the pellet stove heat the master bedroom is a couple of degrees cooler than the living room. But once I switch back to the heat pump as primary heat source I expect to see a more uniform temperature level throughout the house. With the pellet stove heat the floor is only about 2 - 4° cooler than the room air.

The return air enters the attic through registers in the ceiling and then is drawn down into the air handler from the attic.

I haven't used cooling yet. I hope my ERV will take care of a good share of the summer cooling load. It's in the attic and dumps into the return air plenum there. Based on a few warm days in November I may have to run the ERV for cooling any time the outdoor temp is above 50F!!!

From Christmas to now, about 58 days, I've used about 1200 lbs of pellets. That's about 20 lbs/day. At $250 per ton that's about $2.50 per day and about 160 - 170k Btus/day. Temps have ranged mostly from about 20F to 35F in that time.

Curiously at $75/mo in aux heat (pellet stove) you're spending 2-3 times my average design usage of electric aux. coil, and that's if your time is worth nothing. I hope your high end ASHP and pellet burner cost considerably less than geo.
Not criticism, I mean that only as a reminder that there is no free lunch.
A blogger here (I mentioned before) went to the wood boiler for his indoor pool and enclosure. More than a little part of our conversation was his contribution to the job of heating these things.
Many trades are made when budget meets comfort. Pick which tab you want to pay.
If we do get 30% for geo with no cap, it might be no contest (though I think I saw a blurb somewhere on solid fuel credits as well).
J

I should have been more clear that the only heat in the house the last couple of months is the pellet stove, except maybe Sunday night when it runs out of pellets. HP controller is set 2° below the pellet stove for now. I'll be switching back to HP full time when my pellet supply dwindles to an amount easy to store for next year.

Total heat load for the house the last couple of months, according to pellet consumption, has been on the order of 6 to 10k Btuh. This has been supplemented during the daytime by worker body heat, incandescent lights, and power tools. The stove seldom runs from about noon to evening. It's a small stove, rated for 1500 sq ft, 8k to 30k/hr output. It's always set to run on low.

Joe, I really like your idea. If his Manual J calc shows 5 tons heating and 3.5 tons cooling then couldn't he even get by with only a 2 or 3 ton water to water unit for the backup in combination with the 3.5 ton water to air unit? 

As you said nothing in the law specifies that the backup heat needs to be resistance or gas and a geo backup would actually be more in line with the intent of the legislation.

In actual practice couldn't he use the water to water radiant for heat in mild conditions and once the outside temp reaches a certain point the water to water unit could be set to run 24/7 with only the air unit cycling on/off as needed. That way his floor is always warm and the units should run very efficiently.

that was my thought Greg. Frankly it is the way i would design any in floor radiant system....fossil or geo.
j