FiiO SP3 BT do not wake when needed?

I have a set of FiiO SP3 BT speakers on my desk connected to a PC by Optical. I use headphones on my PC 80% of the time so there can be quite a long time between the times the speakers are used. When I try to switch to speakers, the FiiO are often 'asleep' and do not automatically wake up - I have to go and press the power switch.
I have turned OFF the 'Power saving mode' in the App but this still happens. How do I configure these so they are available immediately?

Previously when using the RCA input, there was no such issue and the speakers would become available after a short pause (waking from some kind of sleep state I assume?). However, the optical input is needed because I get electrical noise / static on the speakers if I use RCA in the current setup :/