thanks, Crane!
i just re-read the owner's manual and realize I can do it that way.
Is there a noticeable alteration in tone or power loss when doing the mis-matched way over using two 8 ohm loads?
Probably a bit of power loss, but I bet you won't notice it.
But never do it the other way : plug a lower ohms cab in a higher ohms output. This will harm power tubes and/or output transformer.