I ASSURE you this star does not, in general, eat detritus.
These sites are trying to SELL you a star and therefor it is sold to you as something you need. This is not necessarily intentional. Historically these stars have been sold in clean up crews and stores just don't know any better. They are counterproductive to a sand bed and eat the critters that DO eat the detritus.
I've studied brittlestars, and know many seastar experts. Let me assure you they do not eat detritus. If they ate detritus, they would not starve to death as most do. They would survive in nearly all tanks, even small new tanks. They would probably readily adapt to eat other foods. They do not. Most information that you will find about seastars on commercial websites is at least moderately, if not completely, wrong. They are using outdated and not scientifically sound information.
I encourage you to TRY and spot feed it but note that very very few will take to this. In fact, I haven't heard from anyone that has said yes, they SEE it consuming what they have tried to feed it.
Also, note that brine shrimp by itself - especially if frozen, is not a suitable diet for long term. It is a nice treat, but it is nutritionally very very poor. Try also mysis shrimp or other frozen foods. At the very least you need to soak the brine in selcon, zeocon, or similar supplements.