Solo 401(k) + Cash Balance for Schedule C

This one I'm pretty sure is easy, but I just wanted to make 100% sure since someone asked me.

Can a sole prop, schedule-C have a solo-k AND cash balance plan?

Yes. 

What I thought, just wanted to confirm.  Thanks!

But be aware that it is highly likely that the employer contribution to the K plan must be 6% or less of net compensation or else the plan sponsor will run afoul of 404(a)(7).

Exactly - we do these all the time: deferrals, catch-up if eligible, 6% PS (be careful to use correct "compensation") and max CB. And if they have the income to support  it, do some voluntary after-tax up to the DC 415 limit and then in-plan conversion to Roth.