I have 3 combo amps each with a single 16 ohm speaker. baffles the heck out of me why Marshall would recommend a 2x12 8 ohm ext cabinet. I want to run both the internal speaker and the ext cabinet at the same time. I would like to put 8 ohm speakers in the combos to match the ext cabs. I have a JCM 2000 DSL 401, a DSL 40cr And an Origin 1x10 20 Watt. Can a16ohm speaker be upgraded with an 8 ohm speaker in these combos and if so what speakers would you recommend. Any additional suggestions or information is most welcome.