I would think that it would depend on the retailer, what you are looking to buy, and how much you are willing to spend.
If you were looking for a pair of speakers and amplifier that listed for say $15,000 total, you may have the dealer give you $4,500 off for your gear.
Now keep in mind, that if you had nothing to trade in on the same items, the dealer may just knock of $3,000 to make the sale. So in essence, you would only have gotten $1,500 for your amp/speakers.
If you were looking for a pair of speakers and amplifier that listed for say $15,000 total, you may have the dealer give you $4,500 off for your gear.
Now keep in mind, that if you had nothing to trade in on the same items, the dealer may just knock of $3,000 to make the sale. So in essence, you would only have gotten $1,500 for your amp/speakers.