There are a bunch of "bluetooth audio transmitters," but they range from way too cheap to have decent quality to way too expensive. Your best bet is to check out what Bose offers and match your stereo's output capabilities with something they make. Here's the thing: if you get an inexpensive Bluetooth transmitter, you could get decent sound through decent 'phones, but if you want to get anything like what your Bose headphones are up to, you'll need a higher-end transmitter.
My first step would be to start looking at Crutchfield, B&H Video, etc., with "prosumer" products and start narrowing down what you're after. Don't be surprised if a transmitter that supports the range your headphones do costs as much as your headphones did.
On the other hand, if you're not as picky about "perfect audio reproduction," there are products like Logitech's Wireless Speaker Adapter. It's around $40 and seems to work well for most people, though the reviews don't mention much about sound quality and I can't find specs for the frequency or dynamic range it supports.