Warden is a crazy sub, but keep in mind the Ti pro has a larger coil and more BL product, so two of them are pretty stiff competition against anything, even if its neo. You'll want to replace them with two of something else (not one) if you want to even try and maintain that kind of power handling. The 4HP handles more power than 3" coils so you'll need more sensitivity to make up for that, or simply more motors of something else. If you're serious about a good upgrade from Two Ti pros and you want more SPL, honestly two 18" TC Pro 5100 is a solid choice. It actually gets louder than the 15" Ti pro by about ~4dB off the same power and has a lot better sound quality, higher xmax, lower inductance, much less and AC modulation. It won't handle as much power, but it does have a 4" vc and more sensitivity, but it's also extremely durable so you will get an increase in SPL. They should be OK with a 2k-3k amp on each woofer.