One of the major selling points of the first generation Home A/V pack was (like the rest of the Zune line) its future-proof ability to work with current and expected products. One way in which this was accomplished was through a removable plastic insert that would correctly size the Zune holding area to your particular model. The second generation followed up on this idea, featuring three sizes of removable inserts (see video) and a sliding dock connector to fit all of the current models.
If you still have a first generation dock or don't feel like shelling out the cash for the whole new system (you can find them for cheap all over the web—I got mine from eBay last February for $40), you can easily "upgrade" it to work with a second gen Zune. Just grab a long, flat object like a butter knife or screwdriver and insert it into the slot at the back of the remote well. Pry until the entire top piece comes off. Be warned that there is a glue between the top piece and the dock, so it might be a little sticky.
I'm not sure if this works with 4s or 8s, but you can give it a try and see!