I just got our first Sire Marcus Miller in the shop for repair.
I talked to their support department about the preamp problem I uncovered. They were very easy to reach and quick to offer a replacement when they get restocked from overseas. So that's a good sign.
In the meanwhile, I fixed the original preamp at component level and resoldered some bad switch wiring problems causing shorting between active and passive selections.
Overall, at first glance I'd say it's a great deal at the under $500 price point. Much nicer than some of the other problem import basses I've seen for more money like the Brubaker Brute.
After a good setup and fret leveling, this appears to be a promising choice for a budget-minded 5-string.