The simple answer to resale value on nearly anything is to buy used. Speakers especially because there's so little wear from use. Other than obviously damaged cabinets or drivers there's nothing to go wrong. Let the seller absorb the depreciation, which is very steep the day you take delivery on new speakers.
On the other hand if you simply must have the latest and greatest, which is perfectly fine, you have to discount resale value as a consideration. And that being said, when purchasing new, well known and well respected major brands will have the least depreciation, but you're always going to take a big hit on resale. The other strategy is to keep new items for a long period of time, which decreases the importance of resale value. The best advice I can give to folks buying a new car is to keep it for 10 or 12 years.