You could do well to ask them to update that firmware. I suspect eventually they'll push it out to all, but I know if you request it they will push it to you now. They did for me.
When you call they don't really seem that aware of the process, but I had more luck when filling in the form
HERE If you then select the "Got a Question or Request" option and ask them to push firmware BUS_2.37.17 and quote your account number you should get it. They gave me a date about 4 days ahead when they would do it. For me it happened late on the day they quoted - around 22:30.
Since that version was pushed I have had no stability issues.
Do note though that after a few days the Superhub web GUI will likely become unresponsive - that happens with both versions of the firmware and is due to a low memory condition on the SH1. It does not affect network traffic though, just the ability to manage the device - fixed by turning off & on!
Hopefully they will be keen to upgrade all the old Business SH1's to the new Hitron device when it supports a routed subnet fixed IP option, that currently they only offer with the SH1
Regarding your Asus - no issue with that.... I have much the same config, except am using a Cisco router.
You could connect your asus to another port on the SH1 and configure the WAN address son the ASUS as static and make it the next available fixed IP in the block they supplied, with a 255.255.255.248 mask.
then turn off Wireless on the SH1 and turn it on on the Asus. Then have the Asus provide DHCP and NAT services to devices behind it.
Depending on how the Asus works you might also need a static default route pointing to the public IP address of the SH1
I have virtually that setup now working perfectly. My mailserver though is on a 192.168.x.x address behind the Cisco and I am doing a static NAT for that on the Cisco. Using one fixed IP for general browse traffic and another for the server.