If it's just going to be a JRiver MC server, then you're sorta wasting your money on the RAM. On the other hand, 2 GB of RAM for a Mac running any OS after maybe 10.5 or 10.6 is a teeny tiny amount of RAM. You really need a minimum of 4 GB in a Mac to have reasonable performance running more than one program. Running MC alone, you might be ok, but it's really hard to say. Mostly because NO modern Macs come with less than 4 GB, so it's hard to get impressions about how it works with less than 4 GB.
But you've already bought the RAM right? ...and 8 GB of RAM is cheap now. Less than $100 I think.
So be happy with your gifted Mac and MC.
Brian.