MBC is not built to handle volumetric responses. The area of volumetric responses with choice menus and multi-response gets pretty messy. It's been complicated enough to build the MBC software to handle the huge variety of choice-based MBC-type problems. Maybe someday we'll be crazy enough to think we can extend the software to handle volumes. But, it's a nasty area. There is a good paper written in the 2010 Proceedings by Tom Eagle. I'd recommend you take a look at that one. With an extra layer of effort, one could take results from MBC and build additional OLS regression models on top of those results to extend it all to volumes. But, it's tedious work if the menus get very complex. This would be work outside of the MBC software, though certain outputs from MBC could be useful as a starting point (such as the Excel simulators based on choice probabilities that MBC automatically exports).