On the other hand, I don't think that a good 16 channel mixer will be less than the cost of a jamhub (based on what I just saw).
I'm thinking lower end than A&H or used. Behringer's 16 channel is roughly $300 and you can find a Mackie 1604 or Yamaha used for around that price as well.
Probably four for vocals and maybe one or two for drums.
If you're all wearing headphones how do you hear guitar & bass?