The headphones are able to store up to 8 devices in their pairing history. However, they will only auto reconnect to the 2 most recently paired devices, whether or not it's a dongle, a smartphone, or the built-in Bluetooth of a PC, as long as that device had Bluetooth enabled prior to powering on the headphones.
If the 2 most recently paired devices are not nearby/powered on, we can slide the power button on the headphones to the pair position ONCE, then they will start connecting to the rest of the 6 one by one. We don't need to connect them manually.
If you want to clear the pairing history of the headphones and pair it to your two most used devices, you can refer to How to Factory Reset / Clear Pairing History of the Aria Series Headphones.