I googled it and this house has both. Can't tell if there is an adapter or not - might be a question for the gutter supplier.

I am with you. Not a fan at all of the crimped gutters. At least the K gutters sort of look like crown moulding. . . the crimped gutters are not my fave ;)

Here is a link that might be useful:

athensmom, you're awesome. i'll see what my builder comes back with and post back.

The round spout that will fit the flat bottom of the K-style gutter doesn't have the same capacity to handle water that the rectangular spout could. 3" round is less area than 3x4 rectanglular. Same for 4" round vs. 4x6.
Casey

Round downspouts/leaders are most commonly used with half-round gutters but the "drop outlets" that are cut into an aluminum K gutter are made in square, oval and round.

The reason rectangular shapes are so commonly used for gutters and downspouts is that they carry more volume for the sizes typically used. Make sure the gutter has been properly sized for the roof area and your climate and that the smaller round downspouts will not slow water flow in the gutters.

I learned today that the crimped downspouts are crimped because they help water flow and also help stabilize the downspout so it doesn't deform or crush as easily.