2000S cabs came in different impedances. From the factory they all were loaded with matched JBL D140F's which were available in either 8 or 16 ohms, so 32, 16, 8, or 4 ohms is possible, although I can't imagine why one would be wired for 32 ohms from the factory.
Your amp is configured (or at least was configured) to have either one 8 ohm cab, or two 8 ohm cabs, but you can run it with one 4 ohm cab if you use the extention jack. The amps can be configured to run a single or pair of 16 ohm, or a single or pair of 8 ohm or a single 4 ohm cab(s) with minor surgery.
There are numerous threads here regarding the impedance of the old Sunn tube amps, a search will get you everything you are looking for; but in essence the amps have 16, 8, and 4 ohm taps available on the factory output transformers, and the jacks default in parallel to the lower impedance of the two out of the potential three taps they are wired to.
