Put in a {debug} to see what variables you actually have.
I guess that as its a profile page there isn't an $item array and you need to do item_id=$_profile_id in the rating call.
Dependent upon the skin you're using, its maybe all in the artist.tpl template.
Adding another tab is likely as easy as adding another ul/li structure with an appropriate option in the URL call. The smarty code can then check for the option and do a jrCore_list with order_by profile_rating_count or profile_rating_average_count
hth
Pa
updated by @paul: 12/22/13 09:59:47PM
Watch this space!! A conversion module that runs on its own server is in progress and we'll also be offering a 'conversion' service.
updated by @paul: 12/20/13 10:06:29PM
jrSeamless doesn't support random ordering atm. I'll see how easy that might be, but there might have been a good reason that I didn't do it in the first place!!
jrCore_list should work though. Try order_by="_created RANDOM"