I asked Carol Adelman about putting them in pots and she recommended not to because they freeze/thaw/repeat. She said it would kill the root unless you can store it somewhere to control that process. We're a zone 5, verging on 4B so quite a bit colder and Colorado goes through some bad freeze/thaw cycles every winter, you might not be as bad. I've seen posts from people further south that raise them in pots with no problem.
Mrs. Adelman did suggest I use something the size of a halved wine barrel if I did decide to try pots.
Hopefully someone also in zone 6 will respond with their experience.

I thought about the exposure to the elements if they were potted. If we have another winter like last year, I am sure they would all die.

I have eight of them so that would be a huge amount of room with wine barrels. I just don't have anywhere else for them so it's a dilemma.

Linda

Do you have a spot where they get direct spring sun before the trees leave out? They do fine and bloom well as long as the leaves of the trees do not shade them while they are growing in the spring. If they are shaded after they bloom, they may develop powdery mildew. When that happens, you just need to cut them down to about 3 inches and discard those parts. I have seen someone near me grows the peonies in such an area and have very good success.

They are late bloomers and by the time they bloom the Prunus is in full leaf. I've never had PM at this house which is interesting given how much shade there is.

Linda