A 401(k) is not an IRA. Contributions to the solo 401(k) are not to be entered anywhere under Deductions & Credits. It is to be entered in the business section under Wages & Income.
Contributions to the solo 401(k) do make you covered by a workplace retirement plan, so that could affect you your your spouse's eligibility to deduct an actual traditional IRA contribution. The self-employed retirement deduction that results from the contributions to the 401(k) does reduce compensation available to support a traditional IRA contribution by you or your spouse, so it's possible insufficient supporting compensation could make one ineligible to contribute to a traditional IRA.
