That is strange. There doesn't seem to be any switches or volume control on the Logitech to complicate things - it's just a straight-through receiver. I take it there is zero music sound appearing at all - no matter how quiet - when connected to the Quad pre amp?
It suggests only several options, all fairly unlikely in isolation:
1. The Bluetooth signal is not being received when the Logitech is in the lounge. I think the manual says the blue light will be on if a connection is established to the computer. So is the blue light on when in the lounge?
2. The RCA outputs of the Logitech are faulty
3. The interconnect cable broke suddenly
I assume when working with the computer speakers that the 3.5mm output on the Logitech was being used rather than the RCA outputs?
When the Logitech is in the lounge, do you have anything that you could plug into its 3.5mm socket e.g. a pair of headphones? Or temporary move the computer speakers to the lounge. That would rule out the first option above.