If your main amp's speaker connections inside your speaker's are equally split or "Y'ed" to each driver's crossover, it should be doable. Your "extra" pre-amp gain is key. Splitting the pre-amp signal has to meet the input sensitivities of both amps.
You would disconnect your speaker's "split" leads to the bass driver's crossover, and leave the upper driver(s) connections intact to your current amp.
Then, connect your new amp to the bass driver's input crossover. If no input crossover is used, then, connect the new amp directly to the bass driver. How each speaker section, bass and trebles, responds to gain from two different amp's is a balancing trick. The input sensitivity and output ratings of both amps should be matched carefully to even out the bass and treble responces so different levels of gain result in even volume level gains for two different amps.
If bass and treble balance is a problem, I'd consider adding a good quality attenuator or volume controller on the bass driver like a subwoofer's gain is adjusted for different recordings and rooms. A higher end Niles volume controller just before the bass driver connection may do it for you.
If you have enough preamp gain to split your preamp signal, another way is using a Behringer DEQ 2496. One cleanly split preamp signal pair goes to your current amp and treble drivers, and the other split pair to the Behringer's analog inputs. Then, use the analog OUT's to connect to your new bass amps. Connect the new amps leads only to your bass drivers. The Behringer's analog outs/ DAC's in lower frequencies is quite good. It also adds a good volume controller only effecting the bass driver, plus, EQ adjustments. You can use the parametric EQ and adjust +/- any frequency the bass driver reproduces. Then, adjust the main Behringer's main volume to the bass amp.
With the DEQ 2496, you can leave frequency settings to flat (leveraging your internal crossovers)or add in the parametric EQ to your taste. It also has a 12 dB boost to offset marginal preamp signals to better meet the amps input sensitivity.
I'm not a engineer, but tossing ideas out as a consideration.
You would disconnect your speaker's "split" leads to the bass driver's crossover, and leave the upper driver(s) connections intact to your current amp.
Then, connect your new amp to the bass driver's input crossover. If no input crossover is used, then, connect the new amp directly to the bass driver. How each speaker section, bass and trebles, responds to gain from two different amp's is a balancing trick. The input sensitivity and output ratings of both amps should be matched carefully to even out the bass and treble responces so different levels of gain result in even volume level gains for two different amps.
If bass and treble balance is a problem, I'd consider adding a good quality attenuator or volume controller on the bass driver like a subwoofer's gain is adjusted for different recordings and rooms. A higher end Niles volume controller just before the bass driver connection may do it for you.
If you have enough preamp gain to split your preamp signal, another way is using a Behringer DEQ 2496. One cleanly split preamp signal pair goes to your current amp and treble drivers, and the other split pair to the Behringer's analog inputs. Then, use the analog OUT's to connect to your new bass amps. Connect the new amps leads only to your bass drivers. The Behringer's analog outs/ DAC's in lower frequencies is quite good. It also adds a good volume controller only effecting the bass driver, plus, EQ adjustments. You can use the parametric EQ and adjust +/- any frequency the bass driver reproduces. Then, adjust the main Behringer's main volume to the bass amp.
With the DEQ 2496, you can leave frequency settings to flat (leveraging your internal crossovers)or add in the parametric EQ to your taste. It also has a 12 dB boost to offset marginal preamp signals to better meet the amps input sensitivity.
I'm not a engineer, but tossing ideas out as a consideration.