Here's how to connect two ProReck Party 10 Line Array Systems so that the volume is consistent with both (True TWS Mode):

Party 10 has TWS function and can be connected to TWO party 10 via ONE Bluetooth.

1. DO NOT connect your phone or bluetooth device yet your mobile phone.
(If you do, it may/will automatically connect to a certain speaker, and you cannot use the TWS function)
2. Press the MODE button for both Party 10's to switch to Bluetooth mode.
(You will see "BLUE" flashing on both screens)
3. Next, long press the pause/play button of ONE speaker (I do it with the one that I am inputting sound to).
At this time, the two speakers will be connected together, and one will be displayed as "A" and the other as "B" on the screen. This shows that the two speakers have been connected.
4. You can now open your mobile phone/bluetooth device, search for Bluetooth signal, and connect to the combined (single) bluetooth marked "Proreck" at this time.
5. Using this method, ONE mobile phone/device can be connected to TWO speakers via ONE Bluetooth.

I have found:
It is also best to put into TWS mode even if you are just using it with a line-in input as well
when you are Line-In/Line-Out between two speakers (you get consistent volume on both this way) ...

Sounds interesting.

Dude, those systems are dirt cheap and fucking amazing; I have 2 of them ...
I'll do a write-up/review of it/them in the next day or so ...

http://www.proreck.com/products_detail/productId=71.html