I've seen a few pictures of and/or comments about 8-strings here, but I haven't noticed a thread devoted primarily to the 8-string. So I thought I'd post some of my impressions about the S8, especially in context of my other 8-string.
I much prefer the (hi-gain) pickups on the Ric versus the active pups on the Tune. I generally prefer passive to active anyway - although active pickups can be cool and can give really bright sounds, I prefer the way passives interact with pedals and effects better, especially distortion.
The order of the pairs of strings is an interesting issue. The Tune has what I consider the "standard" arrangement - when downpicking, one hits the higher string first. In the recent book about John Entwistle's bass/guitar collection, he even says words to the effect that Rickenbacker got the string order backwards! (Look at the page with the 8-string with the funny squiggly headstock - great book, by the way.) I did find it harder to accurately fret both strings with the Ric, though I didn't have adequate time to woodshed with it. I liked playing fingerstyle with the Ric better - with the Tune, I find that when my finger comes to rest on the next string, the higher string rings out. Again, a deficiency in my technique no doubt, but I like the fact that the Ric doesn't require different muting techniques.
The Ric is definitely a bit neck-heavy, probably due to the fact that all the tuners are the same size. The Tune uses guitar tuners for the high strings. I realized that I've got similar pictures of both basses, so I'll end this with pics (which I know people here love!)
Feel free to post your own thoughts/comments on 8-strings...
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(another excuse to post my proudest moment). After playing a full gig on the s8 just after buying it I suffered some decent blisters which is abnormal for me. Two nights later my band had a very important gig (for us anyway) and the blisters I had gave way leading to this mess(my 4003 MID)..... 
