The Infinity Beta is the best speaker at a reasonable price for super full range sound. The Bass uses the same 12" drivers found in the orginal Kappa speakers. The main thing to keep in mind is these speakers need a great deal of power on the bass! Infinity claimed the IRS had a 2000 watt amplifier built into the bass. That being so, I would say that something like a Bryston 7B would be the least power I would recommend.
I always liked the RS 1 and 1B better for the midrange and highs over the Beta and the Beta better for bass. Some have discussed using two bass networks, rather than one, but I think the 12" woofers in the Betas make the difference.
Both speakers are great and still today, are among the best speakers out there. The IRS is better; if you need something more than the RS1 or IRS Beta, but can't afford the IRS you can build something in between and that is where the real excitement for me begins!