Assuming that both devices are on the inside of the router, it should make no difference what brand or model of router is being used - the traffic doesn't pass through the router itself, but through a network switch that just happens to be located in the router cabinet.
You should be able to connect that HP MediaVault to whatever device you have with a switch, completely removing the router from the equation.
What I'm essentially saying is that the router was not your problem, changing the router may have fixed it, but that is a side effect of changing the router, and you could quite likely get it working with the old router also.