I have a 5000T and you are correct, a majority of the players (except iPlayer) either do not work, are so slow you just give up or crash the box.
This is a constant theme of many posts on this forum and no amount of complaining to Humax seems to move them to resolving the issues. Instead of owning their own product failings they just blame external forces.
I maybe completely wrong but I believe the product could now be legacy, there have been no updates of fixes for 14 months. There could be a 6000T in the wings that will solve all our issues and a rollback of an updated software bundle like they did for the 4000T a few months after the 5000T was released.
Depending what you are looking for also consider the Manhattan T3-R which by all accounts is much faster but does not have Netflix, triple tuner or a 2TB drive option, however, it does look to be supported with regular updates and improved functionality and they also respond to queries very quickly.
Humax should not be marketing and selling a product which has serious known functionality defects, if push came to shove they are probably in breach of some trading laws so they should get a grip and sort things out.
Unfortunately for most of us on this forum they have already had our money and for us to vote with out feet has little consequence. If potential new customers go elsewhere then that is maybe what will focus some minds.