Well, the answer is easy, though not necessarily cheap.
First, determine what she wants that costs at least $750 clams. Buy her one. Be sure to put it in a fancy box, and supply a nice card and/or flowers.
Wait one week.
Then, buy your desired piece of audio gear. Tell her you bought it from a friend who had terminal cancer, and needed the money to pay medical bills. Have it shipped to a PO Box if possible, so you can bring it home in the back seat of your car (and so it's not delivered by USPS or UPS). While bringing it in the door, ask her if she'd like to sign the sympathy card that you bought him, and if she'd like to go with you to visit him.
If that doesn't work, well, be prepared to sleep on the sofa.