Just tie him to a chair in the middle of Costco or WalMart, and make him watch a JLo/Ben Afleck film while hearing it on one of their demo HTIB systems, when he is crying and beggin for mercy, at his weakest point, play a good sounding movie like Ratatouille or King Kong (any good sountrack multi channel movie), then take him to a B&M audio store make him watch the same movie, through a good set of speakers in his price range, and he will convert.
If all that fails, let him buy the HTIB he wants, or recommend him a worst one, and when your speakers arrive have him set them up with you, make him part of the experience, and in a "I'm superior than you" tone say "I told you so", when he starts whinning about how good your system sounds, and how now he wants to upgrade; just a couple of months after he spent $500.00 for his POS HTIB.