8 Ohm LF driver for M-Audio BX5a Amp???

thinking if I can upgrade to an 8 ohms driver.
Why do you think going to 8 ohms is an "upgrade"? :confused:
You will cut LF power by half :eek:

Since it's a Studio monitor and accuracy is most important, I'd first try to get an original replacement from Manufacturer, and if not possible, would search for an as-equal-as-possible replacement and replace *both* at the same time.

These active cabinets are heavily equalized internally to get as flat as possible response; even fitting a "better" speaker there will not do, because compensation will be way off.