UTM as virtualized guest

Dear forum,

i hope i'm right not having found any prior thread...

I struggle to get an UTM (latest release, ISO-download) running as VBox (4.2.6) guest; VBox-host-machine OS:OS-X 10.7.5.

The guest is configured to have 2 NICs, one of it in NAT-mode, the other in Host-Only-mode, with DHCP-server disabled.
NIC-Driver: INTEL PRO/1000MT SERVER (8254EM)

This is the same config, as a 2nd LINUX-VM is configured like, which is perfectly fine accessible with all its service, while it can access internet, thus a verified configuration actually.

1) Installation works fine, static IP and gateway provided during installation, with IP on same net as the Host-Only-network.

Past post installation reboot, no access to webadmin, nor ssh.

2) 2nd installation made sure to set root-passwd via console prior to initial post install reboot.

After reboot, same problems: no ssh, no webadmin-access.

Local login as root and:
-made sure IP-config is as expectectd,
-link is up,
-iptables temporarily stopped
-root-login allowed in sshd-config
-hosts.deny commented
-routing table healthy (also comparison with other LINUX-VM on same host-only network)
-hostname is reasonable (FQDN, default "host.domain.example")
-on VBox hostmachine all firewalls and AV switched off

But still no access.
Even local access to webadmin via curl fails.

Bottom line: everything that works for the 2nd LINUX-host on same net fails for the UTM.

Currently no idea what could block access.

Does anyone of you could provide me with a hint?

best regards

xorxy