I have used Monster Cable Y adapters for a similar purpose with good results. Try it and let your ears be the judge.
However, there is another consideration. Not all amplifiers have the same amount of gain. In other words, as you increase the volume both amplifiers may not increase in volume at the same rate. This could result in a much different mix at different volumes. Either check the specs in the manuals or let your ears be the judge.
One last thought... If the gain is not an issue, don't assume that you'll get the best sound with the larger amp running the bass. Both of your amps are strong enough to drive the bass, so try it both ways. I'll bet your determining factor will be the amp driving the mids and highs, not the other way around. You'll want the more detailed amp for the mids and top end. The whole point of bi-amping is to relieve the amp running the mids and highs of the burden of driving bass so it can have plenty of reserves for transients where our ears are the most discerning. Let your ears be the judge.
Good luck and let us know how it goes.
However, there is another consideration. Not all amplifiers have the same amount of gain. In other words, as you increase the volume both amplifiers may not increase in volume at the same rate. This could result in a much different mix at different volumes. Either check the specs in the manuals or let your ears be the judge.
One last thought... If the gain is not an issue, don't assume that you'll get the best sound with the larger amp running the bass. Both of your amps are strong enough to drive the bass, so try it both ways. I'll bet your determining factor will be the amp driving the mids and highs, not the other way around. You'll want the more detailed amp for the mids and top end. The whole point of bi-amping is to relieve the amp running the mids and highs of the burden of driving bass so it can have plenty of reserves for transients where our ears are the most discerning. Let your ears be the judge.
Good luck and let us know how it goes.