Avalanche upgrade cartridge for Boxxer, or tune existing?
I'm not too familiar with the Boxxer line, but it looks like they come in both a coil and air versions. If yours is a coil one, have you considered trying a stiffer spring? It is likely the cheapest option, and should help with the bottoming out, and will quicken the rebound for the 'packing down' on small bumps. Replacing the spring is probably the cheapest option too, so it might be worth a try.