I think you can do better than Rel, too. Learn to read the test specs for output and distortion levels... an educated consumer, after all...
And of course your connection is going to recommend what he sells... it still helps him out, moving inventory that he might have on hand. Forgive, but saying that Hsu and SVS are not quality is like saying a Pinto is better than a Camaro.
You got a great deal on your other gear. Kudos. Don't chump out now.
A tape measure and a little Math is all you need to learn the open area volume of your room. LxWxH. To adjust for vaulted ceilings, make it simple:
Measure your LxW. How high is the lowest part of the ceiling? How high is the Highest?
Simple example:
12x15x8 to lowest, and 12x15x12 to the highest. figure volume for the low part, then look at the difference in height, 4', and figure the volume for that and multply by half, adding that to the volume of the room below.
1440'3 + (720'3 x .5) = 1440 + 360 = 1800'3
Once you know the rough volume, making certain you have enough woofage becomes easy! We love to help people get the best gear they can afford! In this case... maybe not that Rel.