Ok - since no one else will answer this question, I will answer it myself - Note - this (finally) works registering against a Broadsoft switch - so some of the things might be unnecessary, but this is what was required to get it working against Broadsoft:
With these settings, the trunk registers and we can make calls in and out - Strangely, SRV lookup is not working - I had to switch to the IP of my provider. 199.168.179.168 is the ip for lax-iad3.masteraccess.com.
If anybody knows why SRV lookup is not working (Asterisk 13.3.1) let me know - but it works ok with the IP.