Audio issue!

I have recently purchased a 2004 Vogue HSE TD6 with a 2012 facelift fitted with an aftermarket android stereo.
The radio works fine and speakers also work but there’s little to no bass what so ever. After inspection I found that the factory fitted sub has been removed along with radio module and sat-nav module, there is a Lear amp still fitted which after some reading up I can gather has remained due to needing a bypass cable for the android stereo to operate with the speakers?

my question is .. to be able to gain a subwoofer back in the car factory or not, what is my best option?

can you get a factory sub to work off an aftermarket android stereo or would I have to go after market?

thanks!

You'll need a pre-amp bass output to send to the factory sub woofer, never used an Android so don't know if that's an option
there's adapters available to convert hi level speaker output to low level sub input, should work in theory but I've never tried it