I'm a sole proprietor, but yes, I think the employer contribution for an S-corp is up to 25% of W2 box 1.
Your husband can contribute to a solo 401(k) (and the receive the same employer contribution match), but only if he is paid by the business. If he works in the business then it seems likely that it would be a good idea to pay him a reasonable wage/salary. Make sure you can justify the amount you pay him based on the amount of work he does and the skill level required -- basically, pay him what you would pay an unrelated person to do the same work.
If you're currently taking some of your business income as an owner's draw (not subject to FICA taxes) then shifting some of that to income for your husband will increase your FICA taxes both for him and for the business, so you'll have to see if the 401(k) deduction makes up for that. This will also help him earn social security credits, which could be good.
It would probably be a good idea to work with your accountant to put some actual numbers to all this based on your situation.
