can one employee have two super accounts ?

Hi Deb

Salary Sacrificed Super is not the same as the standard employer super (SGC)
Unlike SGC, SS amounts are deducted from the employee's gross pay - reducing the PAYGW amount - to obtain a tax benefit.  This is classified as Reportable Employer Super Contributions (or RESC) & needs to be configured correctly for both the PAYGW tax & RESC to calculate & report accurately.
You need to set up a Salary Sacrifice Payroll Item for this additional fund.  You can specify a % or fixed $ amount on the employee's record.

Yes, you can add as many Super Payroll Items as you like to an Employee's record.

In their "Super Details" section, just enter/add the SS Payroll Item on to the next line in the "Item Name" box (under their existing Super Payroll Item)