I've got an IPSEC VPN working between an Astaro v8.305 firewall and an ASA.
Make sure to get the lifetimes all set the same on both ends (it's tricky as the names are different on each end), and match all the other parameters. Disable PFS and disable Strict Mode.
I could show you the UTM end, but I don't have access to the ASA.
Turn off 'debug mode' on the UTM VPN settings, and download the log (not the live log) from the UTM and post it here. Posting screenshots of both end's configurations would also be helpful.
I'd also be very interested in seeing how you configured your UTM to success connect to the ASA. I'm also trying to do this (as you know I've created a thread in the VPN section of this forum). The connection appears to be UP and established, but nothing can ping each other behind each endpoint. The WAN connection on the UTM side is handled by a cisco router (and managed externally). They've configured all traffic for the UTM's public IP to be sent to the UTM's LAN IP.
We can successfully connect using the Sophos VPN client on a laptop without a problem. Just the Site-to-Site is having the issue.