Not sure if anyone has an answer, however any help would be most appreciated and I imagine a few people have had to deal with this when they transitioned to UFB.  Anyway, the issue and background is this:

1.  I have Snap UFB and that enters the house in the garage and the ONT is connected to the FritzBox 7390, which is also in the garage.

2.  I have Cat 6 cabling from the FritzBox going to (i) my telephone system (FritzBox for SNAP's VOIP and we use the built in messaging system to send the voicemails by email to our mobile phones) and (ii) to my office.

3.  In my office I have a Cat 6 cable running from the wall plug to my ASUS RT-AC66U to which I have connected by Cat 5/6 cables the following:

(a) Desktop PC
(b) Windows Home Server (WHS 2011)
(c)  Printers

4.  I have wifi switched off on the FritzBox (its lousy and would be no use from the garage) and I use the ASUS to do (i) wifi and (ii) manage the LAN and therefore it does the DHCP (it is far better at managing this than the FritzBox).

5.  Because I'm using the ASUS to do DHCP there is of course double NAT as the Fritzbox also does DHCP and assigns the ASUS with an IP address within the Fritzbox's subnet (e.g. 192.168.178.20).  In the normal course this isn't a problem and connection to the internet etc. is great, however I'm trying to setup Remote Access on the WHS 2011 Server as I'm going to do a few things like create a Wordpress blog for my wife, use Plex to connect externally etc. and with double NAT in place this won't work.

6.  I've tried the following remedies with varying levels of success:

(a)  Disabling NAT in the FritzBox, however this also disables DHCP - this kind of works for a bit, however as the DHCP server in the FritzBox is also disabled by this it causes the connection between the FritzBox and the ASUS to crash after a period of time and you can't even log into the FritzBox without physically attaching it to a laptop/PC.

(b)  By adding the ASUS as an "Exposed Host" in the settings of the FritzBox (the FritzBox does not have a DMZ) - this is the best result I've had as when you run the setup of Remote Access on the WHS2011 Server it says that everything has been set up fine (i.e. no double NAT issues) however when you try to access the WHS2011 Server by remote access you get a screen with a FritzBox login which asks for a username and password rather than getting the server's login page.

(c)  Portforwarding - not sure what I'm doing wrong here but can't get this to work at all as I know you need to set up port forward rules on both the ASUS and the FritzBox but I can't seem to set this up right.  Also, my concern is that even if I do set this up right I'm still going to get the issue I had in (b) above with the "Exposed Host" and seeing a FritzBox login screen rather than the login screen for the WHS2011 Server.

Prior to having UFB I simply had a D-link ADSL2 modem in front of the ASUS and I was easily able to port forward within that to make it all work and I thought with UFB it would be just as easy, but alas it doesn't seem to be. 

I have a spare ASUS RT-N66U lying around and I have given thought to using that instead of the FritzBox and I would let the N66U do all the DNCP and just use the AC66U as a wireless bridge, however I'm not sure how easy the SNAP VOIP will be to set up on that and I imagine we will lose the benefit of the answering machine and emailed voice-messages which my wife loves, so this would be a last resort.

Any help would be really appreciated.

Cheers
Go Highlanders