Yes, you may use your store credit for a Home Audition unit if the security deposit amount matches with the store credit amount.
If you are ordering for a Home Audition unit of a higher value than your available store credit, make sure you pay the difference online and not via Cash on Delivery.
Please note: In case you decide to not buy a new unit and want a refund, only the difference amount that you paid online will be refunded. The store credit will not be refunded to you.