I have a half back mid 80's mesa 4x12 cab which needs a new blackshadow 90 watt speaker. It is a stereo cab with 3 inputs. one for 8ohm mono and two for 4/16 ohm stereo. Im figuring I replace it with a 8ohm...am I right? The cabs locked at a practice space and I want to order before practice in 3 days. I also use this as my Biamp rig with a seperate tube head.