I've found that even older speaker docks will often readily accept the newer iOS devices such as iPhones & iPod touch by simply inserting the Griffin charge converter inbetween. Here's a link to the product you should investigate. Seems like it's not carried much anymore unfortunately.
Useful info in the review section-
I'm thinking of getting an ipod classic 7th generation. The info on the speaker docks that I read about mentions compatibility with 6th generation but not 7th. Then I read somewhere that the 7th generation is really the same as the 6th - just more capacity.
Does anyone know if the place where these would fit on the dock is the same on both models of these Ipods? I'd hate to buy a dock and find it to be incompatible.