No, your basis would be $6,000, not $7,600.
The 1,600 from the 401K remains pre-tax, therefore no basis. If it was a distribution and became taxable, then it would add to the basis.
The wording is a bit misleading, but I think it means any after tax contributions in the 401K that would have basis in the 401K, that would carryover that basis into the new account. Pretax contributions don't get basis until either distributed or converted to after tax.
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