sRGB is NOT 8-bits..... it's got nothing to do with bit-depth and is just a (very slightly) smaller colour gamut. In an ideal world you'd shoot in Raw, open it (from your conversion software, like Adobe Camera Raw) as a 16-bit file, then convert to AdobeRGB before processing and printing. However, there's a problem ...... a lot of editing software can only edit in 8-bits (aprt from cropping and some basic things). Even Photoshop CS5 has some limitations. (PaintShop Pro Photo professes to do 16-bit editing - but they don't make it clear just how good it is)
In practice, though, you won't see a difference in a print in AdobeRGB, compared with sRGB, unless it's made on very sophisticated professional hardware (not the kind you buy in the High Street, but some of the high-end printers can make use of it).
Otherwise, Jpeg is definitely
not the way to go if you want the best quality colour or detail.
So there are a couple or points to remember....
1. Yes, AdobeRGB has a wider Colour Gamut than sRGB..... but you won't see a difference on almost any home printer.
2. You'd need to keep away from Jpeg completely - it's only 8-bits (even though it can use both AdobeRGB and sRGB).
3. Unless you have a sophisticated printing business and a very serious printer, you're not going to get more than 8-bits from your printer.
Cambridge in Color is a great site for detailed information (sometimes too much!).... but
check out this page.