I have Elementary OS Loki installed on my Dell XPS 15, I've got it paired to my UE Boom 2 and Bose QuietControl 30, but they aren't showing up as a possible Sound output.
Their indicated type is Headphones.
I was able to work with them on my old 17" MacBook pro with Elementary Loki.
To get Elementary OS installed I followed the following blog post, which included a bluetooth fix. https://ubuntuforums.org/showthread.php?t=2317843
Update: I think I got it working for my Bose QC... Advised by the following question I installed
pulseaudio-module-bluetooth. Maybe that helped. I did need to reboot and re-pair.
Strangely enough I still can't get my UE Boom 2 to work.
Update 2: Seeing that lot's of people switched out the Killer wifi card in the XPS 13 line (in my case the Killer 1535), for the Intel 8265, since intel drivers would work better on Linux I thought I'd tried the same. It didn't went well I'm afraid, I had to upgrade the Kernel from the default 4.4 to +4.6 for it to be recognized. But then the bluetooth connection was disconnected frequently, usually after a few minutes. (I also tried removing tlp and downloading new drivers from https://git.kernel.org/pub/scm/linux/kernel/git/iwlwifi/linux-firmware.git but that didn't seem to help.
Update 3: I've upgraded to the latest elementary OS Juno (based on Ubuntu Bionic 18.04) and now everything works! On a fresh installation I can easily pair with my Bose QuietControl 30 and UE Boom 2 and use them as sound output. No extra applications or tweaks required.