TubeNet

I didn't know there was an "XXS". I'm assuming the XS is the regular large piston model and the XXS is the small one. I haven't played the big one in a while, but the small one definitely rocks!

Umm,.... one's bigger than the other?
They are different horns with different valve sets and everything.
Like I said, I haven't played a big 3200 in a few years but I was able to play the small one next to a regular 3400 (apparently there is a small 3400 now...). Roughly, the 3400 is kinda like a 186 sound-size-wise and the small 3200 reminded me a bit of a slightly larger 621F. Roughly. This was a couple months ago and although I also played a few MW bass tubas I didn't play them next to each other.
I think with a smaller mouthpiece, the small 3200 pass as a decent bass/contrabone/cimbasso substitute for a tuba player who can't handle a slide though it doesn't seem to do edge as easily as other F's.
The small 3200 also has a main slide kicker with a surprising amount of slide though I think it only goes out. I don't remember if the big one has that. They both have a 4th slide wrap like my old Conn Eb with the 4th slide at the bottom. I don't much care for that.
On the cheaper side of bass tubas, the Cerveny 653/5 F and the St. Pete Eb are both really nice horns. I love the 3400 and small 3200 (and wouldn't mind having both!), but they are quite expensive new.

The Willson 3200 FA-5 (FA-5=Front Action 5 valves) is the name of the older model piston F tuba (the S is for silver). They recently replaced this model with two new models; one small (3200 FA-5 XS) and one large (3200 FA-5 XL). The large one is comparable to the older model.