I have 2 XFLs on a HFi2500d (same guts as a BRZ2400) and it's extremely loud. I'm fairly sure I can turn it up louder but I don't want to with my current electrical.
Get the xfl's... I had a single 12 on 1500 + daily and rarely even gets warm. Low as crap too. Very solid subs and would take that BRZ or Rubi nicely..