My understanding is as follows -
Do you appreciate that when you pair something to a Sena bluetooth device it becomes your 'number one' i.e. one press on the jog dial button to connect and commence a conversation (or similar with the SRL controls). When you subsequently pair another BT set, the initial pairing moves to become your 'number two' (two presses on the button to connect) and the latest pairing becomes 'number one', and so on to the capacity of the set
That said, try this - pair SRL1 set with SRL2 set; then pair one of the SRL sets with the SMH10 thus daisy chaining them
On the SMH10 you enter 'intercom pairing' mode by pressing and holding the jog dial button for a few seconds. It then flashes alternating blue and red. Do the same with the SRL set (I'm not sure of the button press combination) and it too should tell you it is 'intercom pairing' They will either pair automatically at that point of pair when you press the jog dial button on one set
Forgive me if I've stated the obvious here but I know people who have used SENA kit for ages and never learnt this