I have a Rumble 500 combo and want to use an existing cabinet as an extension cab. It is an existing Fender BXR 300 combo amp (15", 300watt @4ohms Fender Special design driver) but, I plan to upgrade the driver to one of several Eminence 8ohm options. The Legend CB15, Legend BP 1525, and the Eminence Delta series. I have no use for this amp and figured it would be cheaper to just buy a driver similar to what the rumbles have in their extended cabs. Also, this cabinet is similar in dimension to the rumble 1x15 cab and is vented at the bottom (pictured below the Rumble). Appreciate any input.