Pretty sure it has been mentioned above, but with subwoofers intergration with your mains can be difficult. This is more tricky in some set-ups than others (planars + subs, for example). But the trick is to get a seamless handoff to the sub. Just like between the drivers of mains, the handoff is an area that requires great skill. Only with subs, you are getting drivers not chosen by the designers of your mains in most cases. So search out subs that can integrate nicely. The RELs have a good reputation for this using their speaker-level inputs. And there are a number of subs with DSP capabilities, that might be great choices. Or there are outboard DSP devices (either full-range or designed for subs only) that can also help with the handoff (and mitigate things like room effects to boot).
You are getting a lot of great advice here. You should feel lucky to have Al and Duke (Audiokinesis) on the job.
You are getting a lot of great advice here. You should feel lucky to have Al and Duke (Audiokinesis) on the job.