It seems that the issue here is the "alternative defined contribution plan" rule under 1.401(k)-1(d)(4). You say that the 2 subs were not participating in the original 401(k) plan sponsored by another entity in the controlled group. If the subs were not participating employers in the original 401(k) plan, their employees were not eligible under the original 401(k) plan which terminated. Therefore, it would seem that starting a new 401(k) plan under which ONLY the subs would be eligible would be permitted because the new plan would not be an alternative defined contribution plan because the employees eligible under the new plan were not eligible under the original 401(k) plan. Am I missing something?