An SRV record is unlikely to work because the VoXalot servers are not authoritative for your domains...
I can think of two quick solutions:
-Add a CNAME record pointing sip.yourDomain.com to voxalot.com in which case
123456@yourDomain.com will ring your VoXalot.com
-Take a look at
Voice-over-IP gateway for Google Talk, MSN and Yahoo Users
After creating it forward your registered email to your VoXalot SIP URI with GTalk2Voip (it may help if you're using Google Apps). Also take a look at
Use with Google Apps?