At first I thought it might be one of those BB gimmick where they ask manufacturers to change the model number to have an "exclusive model" and therefore not have to pricematch with anyone, but then I found this thread. It seems is might be an older model (a bit like when MB manufacturers have revision 1.0, 2.0, ...) that has been discontinued. Given the problems reported in the thread, I would either try to find a current model or make sure they have a good return policy in case it didn't work.
They are all basically the same, im not sure what the difference are between the various non XXX versions but they are extremely minor, usually related to software bundles. The XXX versions are overclocked. The one from newegg will 99.9% identical to the one from best buy no matter which of the HD-577A-ZNF* models it is, except it will be a ton cheaper off of newegg.