I already tested Bluetooth speakers with the Cinera and they work great. However, some Cinera owners have found that the 3.5mm audio port on the Cinera tends to work sporadically. Sometimes it works, other times it does not.
Stefan has suggested various go-arounds to solve this problem, which appears to be firmware based. The method that works for me is to enter and then immediately exit the HDMI mode. That works fine but the problem is that, if I turn the Cinera off in the meantime and turn it back on again - even for only a few seconds - the sound is gone again. So I have to go trough the whole process again of entering and exiting the HDMI mode.
One simple solution is to get a pair of Bluetooth headphones. But I have many headphones already. Do I need to buy yet another pair ?
Wouldn't it be neat if there were some type of Bluetooth receiver with a 3.5mm audio port where I could connect any of my headphones ???
But wait... there is ! :-)
Actually, it's full of these on eBay and, even though some fancy ones may set you back ten buck or more, I found a neat one for US$1.98 postpaid that even has built-in volume control buttons and a microphone on it (should you wish to use it with a phone) as well as an accessory adapter to connect it to a sound system.
I just ordered one so can't comment on the quality . But I have been using a similar USB powered one for a sound system for a couple of years that I also paid a couple of bucks and that one has been working great. But the one I have does not have volume controls, a mike or a rechargeable battery so is not ideal for headphone use.