You should have access to the Virgin Australia lounge by virtue of your Business Class ticket and you should have access to the DL SkyClub by virtue of Reserve AMEX in conjunction with your incoming DL flight and as a result of your Business Class ticket (
https://www.delta.com/us/en/airline-...rgin-australia)
This is the page that highlights your lounge access for the VA ticket (
https://www.virginaustralia.com/us/e...ge-access/#LAX)