Sorry I realize my post was kind of harsh, but it is how I feel.
Jack Sondermeyer was the senior engineer on the VCL and VMP. Jack was an old school tube designer from back before transistors were robust. The design brief for the VMP and VCL was to make a serious studio quality audio path.
The tube sweetener design brief was to make one of those cheap tube distortion paths similar to an XYZ that are selling to boys and girls who can't afford real tube gear.
Jack was already retired by that time, so don't know where they came up with that design. I don't even know the right way to design such a product. A tube path that isn't working correctly?
On a related theme, while I was working at peavey I was tasked with clearing out some slow moving inventory... Jack's guys had designed a simple several input tube mixer to use with a premium guitar path to buffer and combine some guitar pedals in front of a tube guitar amp.
Long story short, I had about a hundred of these and I couldn't give these actual tube audio products away because they were too clean,
I even tried to modify them by adding gain to make it easier to saturate, but no love as a tube effect...
Good luck but in my judgement the only thing similar between VCL.VMP, and tube sweetener is the brand, not the engineering parentage.
JR
PS: I had them put the hi Z output in the VMP so you could bypass the output transformer presumably for "lower" distortion. You can always connect the balanced transformer output to an unbalanced input.