so I was wondering if anyone have some tips on wich replacment speaker I can use for the bass element?
It's generally best to use the exact same woofer because the cabinet is optimized for the particular Theile-Small parameters. This is especially critical with ported boxes. It's easy to badly mess-up a ported design whereas sealed boxes are somewhat less finicky.
They got replaced with som unoriginal elements.
You can "model" the performance by measuring/calculating (or estimting) cabinet volume and measuring the port dimensions, and then plugging the Thiele-Small parameters for various prospective drivers into a speaker design application. I've used
WinISD (FREE!). There is also the possibility of modifying or plugging the port(s) and the software will tell you if that's better.
One unknown is if there is bass EQ built-in to further optimize the design, and that won't be optimized for a different driver and your speaker design software won't know about that.
The original (and replacement) woofer sensitivity is also unknown so the new replacement may be louder or quieter.