yahbro said:
would the marshall 1936 extension cab be good?
Yes, if you use it by itself, without the internal speaker. After that, it's about the sound. I'm not too hip on how the different cabs sound, though.
As far as the impedance goes, with your amp, it goes like this:
If you use the internal speaker alone, set the switch to 16ohms.
If you use the internal speaker with an external speaker, the external has to be 16ohms, and the switch on the amp has to be set at 8ohms.
If you use external speakers only, you can:
Use one 8ohm cab, and set the amp switch to 8ohms
Use one 16ohm cab, and set the amp switch to 16ohms
Use two 16ohm cabs, and set the amp switch to 8ohms
The 1936 is designed to act like either one 8ohm cab, or two 16ohm cabs. They call it mono/stereo, as the cab can be set so it has two separate 16ohm inputs. In your case, since it can't be set to be 16ohms mono, you can't use the internal speaker along with the 1936 cab.
It will work if you set it to mono and set the amp for 8ohms, or set it to stereo, use two speaker cables, and set the amp for 8 ohms.
Hope that's not too confusing.