If I can give some free tax advice -
You most certanly can donate them, and get a tax deduction, but it won't be for full retail. The IRS allows "fair market value". For electronics, the most likely place to geet fair market value is usually a blue book (Orion), however Michael Green speakers will not likely be found in a blue book. So, good places to find FMV would be E-bay sales (if any), or if you had them up for auction, the high bid might work. Or high bids on other auctions for the same model.
In an audit, the IRS will probably be amenable as long as you have a reasonable basis for your value, and documentation.
Michael