Actully looking at hub it is only 10mbps so does that mean 3.3mbps to each rio
Right. If it's just a hub and not a switch, it'll share the bandwidth between them. Since it's 10Base-T, that means 3.3mbps per port, though in actuality it'll be unlikely that all 4 will be sending/receiving at the same time. If only one or two of them is communicating, those one or two will split the available 10mbps (minus overhead for ethernet collisions and the like.) I suspect for MP3 traffic, you won't notice any major problems, as 3.3mbps is still a lot higher than MP3 bitrates.