Poor mans ev sx600

[Kevin t]

so afaik the EV sx600 is constructed of a modified sx300 bolted to a modified sb122

I want to buy a sb122 / 121/120 and add it to my trusty sx300 s. The sb has a low pass ~ 120 Hz . So ok in parallel that adds a second 12 in woofer to the sx300 50 -300 hz low pass .
I want to take the sub 150 range out of the sx300 so I can push them a bit harder .
Do I need to feed the 2 cabs from a external crossover bi amp style or install a new 3way passive internal crossover like the sx600 uses . Is there much performance to be gained by just using the stock cabs as is together ?

 

[conanski]

You need an external crossover with 24db filters or you will be disappointed in the results, so if you're gonna add a sub get a modern version like the ZXa1s then you don't need any external equipment and your system looks more professional.