Garyo40,
As long as your H/K receiver has a dedicated line-level sub output, you should be able to use the Crown amp. Although you can regulate the level of the Sub output with your H/K, it's a good idea to use the preamp to give you separate control of overall volume of the subwoofer.
I'm assuming there is no passive crossover built into the Phase Tech sub. If there is, disable it or bypass it. You don't want to cascade two crossovers. You would only need to use one channel of the Crown amplifier for the sub because the dedicated LFE (subwoofer) output is a mono signal.
I have no idea whether Phase Tech subs are good, bad or mediocre. I don't recall that brand being distributed in Canada, and I've not heard one in the US.
Regards,
