https://www.amazon.co.uk/Outtag-Adapter-Universal-230-240V-Connector/dp/B09J4XJM3X
I am using this one but with EU standart plug, works fine on 15V
Don't use it! the subpac has a very specific amper/volt ratio. You should buy 15v 3A universal charger like this one for example
This little guy changes the game for subpac usage: 4-Channel Stereo Headphone Amp
My setup goes from computer > Focusrite 2i2 (though all you need is any headphone jack) > 4 channel amp > 2 subpacs and 2 headphones. Great for listening sessions with a friend or watching movies.
My biggest complaint about the M2/M2x is that the amp introduces a lot of noise and the gain adjustment is a pain to balance against different impedance headphones. This solves both of those problems for about $30. The one I linked is out of stock, but there are several identical ones you can find.
Receiver (1/8 inch audio cord into subpac): https://www.amazon.com/gp/product/B06WLHG7X4/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Transmitter (1/8 inch audio cord in the computer audio out, powered with an empty USB port) https://www.amazon.com/gp/product/B01IV1H1ME/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
There an easy way to tell if aptx is working...if you have noticeable latency, it’s not using aptx! It’s possible your receiver is picking up the computer built in Bluetooth and not the aptx one. Problem solve with turning things off/on and test with a YouTube drum tutorial video (easy to find a delay in the audio/video that way).
Would something like this help? I had a similar issue with my portable setup and ended up placing a passive volume control knob between the subpac and the headphone amplifier, I can now listen to any volume levels on my headphones without worrying about my subpac clipping/blinking red light on the control box.