For that scenario I use the Nokia Wireless Music Receiver to enhance the surround system with bluetooth functionality.

At one end you connect the Wireless music receiver with an appropriate cable to your amplifier AUX or Tape, or to the computer's line in, whatever you prefer ,
and on the other end is of course your faithful N900 transferring the sound over bluetooth.


http://www.amazon.co.uk/Nokia-310-Wi.../dp/B005PN0R1Y

http://nds1.nokia.com/files/support/...-20W_UG_en.pdf

The device has a nice metal touch, uses some standard Nokia power supply pin (the thinnest one) and supports NFC.

Yes there used to be a time that I only had to tap my 808 to the device in order to play its sound (streaming music, movie or file) over my big amplifier connected speakers.
Now I am back on N900 without NFC, but it is still convenient.