Neither the Beam nor the One SL have an audio out, either digital or analog. You’d need to add a Port, which does have an analog output, and then plug that output in to your “ultimate ears megaboom”, assuming it has an analog input of some kind. 

The megaboom is a bluetooth speaker and doesn’t have any plugs. 

Unless the Megaboom is compatible with AirPlay 2, there isn’t any way to play it together with the Beam and One SL.

There are no Sonos devices that ‘send’ a Bluetooth signal (other than BLE for setup purposes), those that are capable (the Roam and the Move) are Bluetooth receivers only.