I am an advocate of bi-amping if the power requirements are high. This way each amp isn't working so hard and isn't required to amplify the entire frequency range with power.
Especially with the Infinity speakers, which are difficult to drive.
I'm not sure if the Infinity speakers have a defeat-able passive crossover that can be removed and replaced with a very good active crossover. If you can't remove the passive crossover, then the benefits of bi-amping are slightly lessened. However, for those speakers, I would definitely bi-amp them.
I'm hearing and reading that Class D amps have made great strides in recent years. I know Jeff Rowland has class D amps, so he wouldn't market them unless he has solved many of the previous class D issues.
I know, the costs is less because the power supply requirements are minimized. (at least, I hope the cost is less).
I would try several amps in my home system before making a decision.
Also, and I know this for fact. Replacing the passive crossover with an active one is always better in my opinion.