Unfortunately it is not possible to cascade the current analogue Tenor’s in the true sense.
The issue is that the two devices will have different IP addresses, so static routes would need to be set up to both units.
The easiest way around this is to use the in-built GateKeeper funtionality of the Tenor. Make one of the devices the GateKeeper for both A800’s, you would need to buy a 8 port GateKeeper upgrade option for the master Tenor to allow it to GateKeep 16 simultaneous calls.
On a positive note, Quintum are soon to release the new AX series which will be available with up to 24 analogue ports. Like the new DX series this will come with the CMS operating system and therefore allow CODEC auto-negotiation etc.
Hope this helps.