halides are great, but that information you received is incorrect. with an 8 lamp fixture that is individually reflected, you can keep sps
on the sand bed, even if your tank is 30 inches deep. those people who are giving you information could have been using junk ebay fixtures or crap bulbs. the same thing can happen with halide lamps at 60 bucks a pop.
i've used both halides and t-5 fixtures over the years and haven't had a problem with either.
that's total nonsense about a 6 or 8 lamp t-5 fixture having difficulty with ballasts also, providing you are speaking of a quality fixture.
these guys must have been using those chinese knock-off garbage fixtures from ebay. if not, they are guaranteed just like halides fixtures.