You can connect to your start9 hosted lightning with Alby rather than using Alby's hosted lightning node. If you go to 'manage wallets' on alby, add a wallet, and select the right box with a list of a dozen different wallets, you will find lndhub, lnd, eclaire, lnbits, etc. Im not sure how you do it with start9, but one way or another you should be able to send and recieve sats with an external lightning wallet app like zeus or bluewallet. Alby can behave just like zeus and bluewallet, and allow you to zap with your selfhosted lightning node directly from your browser.

Once alby is set up with your selfhostes wallet, you can assign nostr keys to that wallet. This way you can switch nostr identities simply by changing which wallet is selected in your alby extension.

The only caveat is that the selfhosted wallet configurations in alby are not stored by alby, its only stored in your browser. You may notice that once you configure alby on one browser the configurarion of your selfhosted wallets carries over to other computers. This is not from Alby storing your information, it's from chrome's profile sync feature keeping your browser extension configurations stored in your google profile.