I’ve never been a fan of biamping with amps that have different input/output parameters, gain and power. If you aren’t using active crossover and not removing (or bypassing) original passive speaker crossovers, your dynamic range will be greatly compromised to listening at certain volume, but not higher or lower to reach maximum coherency and balance not achievable with passive built in speaker crossovers at all. Even after adding any passive volume control you will still have balance and coherency issues at certain volumes!
You’ve already tested your extremely poor idea, now you are in front of choice whether to use original built-in speaker crossover or bypass it pretty much cancelling the speaker voicing and qualities with active crossover which may or maynot benefit.
If you are looking for the increased power, I’d recommend swapping for more powerful amplifier or monoblocks.
The only way of successful biamping that I see is to use 2 SAME amps in case if 2x lower poweramps is below the price of one powerful amp