I'm against treating with products like FeBreeze. Unsure if Oust is the same thing or not.
But here's what they say about it: http://www.oust.com/product.aspx?oust=airSanitizer§ion=howItWorksBut here's what they say about it: http://www.oust.com/product.aspx?oust=airSanitizer§ion=howItWorks
I started using it when my daughter was in an opera in an outside setting in the summer. The guys' clothes would get quite rank and since the show closed about midnight each night, there was no way to clean the costumes for the next day. The crew would spray them with Fabreze but one principal was allergic to the fragrance in it so he made them switch to Oust.
In the car biz, we always used Frigi-Fresh from BG Products to kill mold odor in A/C systems caused by condensate not getting completely out of the system.
If you can borrow an ozone generator, place the disassembled speakers in a spare bathroom and leave the ozone generator on max for a couple of days. Make sure you don't get overly exposed to the ozone - it's arguable whether or not it is harmful to you.
I once bought a pair of surround speakers on eBay that were from a smoker (unknown at the time). When they arrived they smelled so bad I couldn't use them. The ozone generator did the trick, but it took a couple of days.