What cassette would they suggest that you put on? With a 28T low gear, and assuming a short- or mid- cage rear derailleur, there's not much lower you can go. You could add a long-cage mountain rear derailleur and something like a 12-34 mountain cassette, but that's more money, I think. (Also, I don't know off the top of my head what the compatiability issues with SRAM road vs. mountain might be. Don't quote my ramblings as gospel and please feel free to correct them.)

If you want a 46T or 48T big ring, why not? Cross double cranksets are often 46-36. You wouldn't have to change anything else- just shorten the chain a touch. Have you consulted with your shop?