If I have understood you correctly, you are suggesting an AICO interconnected system which can work independently of the Texecom system in the event that the panel fails. In this situation the smokes would work directly off the mains. If the mains failed, it has a backup battery and if all was working, it can send a message to the Texecom panel and trigger a zone. Have I understood this correctly? Assuming yes to the above, I guess that I need to wire in the smokes as conventional mains powered interconnected devices and then also have alarm cable going to the panel?
Yes. I have a set of Aico mains powered smoke alarms, which each have a 9v PP3 battery inside them. The alarms are powered off the mains and if the mains fails they are powered off the internal battery. They are connected together with conventional 3 core and earth cable. If one alarm sounds then they all do. In theory if something should go wrong with the interlink (or a fire burns through the cable before any of the alarms detects it) then the alarms continue to work in isolation. This is standard stuff that all new-build houses are required to have now.
Separately I bought a Aico EI128R relay base. This connects into the interconnect cable in the same way as the smoke alarms themselves do. It contains a set of relay contacts which close when any of the smoke alarms sound. I've then got my alarm connected to this relay, which triggers a zone on the panel. If the smoke alarms go off then the relay switches, changes the state of the zone - and it activates both the internal alarm sounders, and separately sends SMS messages to warn that something is amiss. I'm using a Honeywell alarm panel, though you can do exactly the same with Texecom and ComIP or ComWiFi. The relay base is intended for warden call systems in sheltered housing etc, though does a very good job here.
The advantage of this set up is that everything remains self-contained and isolated from other components. If the Texecom alarm itself bursts into flames, or the cable linking the detectors/relay/alarm etc is compromised then hopefully at least one of the smoke alarms remains operational and wakes you up before the house burns down. The problem with the Texecom etc detectors is that there is too much to go wrong in a very small number of places - such single points of failure on safety critical systems are dangerous.
If you go this route ensure that you keep the mains and alarm cables well away from each other in the AI128R relay. I seem to remember the instructions recommending that ELV (ie 12v) cables are 'double-insulated' - ie insulation over the existing insulation to remove the risk of 12v and 240v wiring coming into contact with each other.
I found Edwardes by far the cheapest for Aico bits. If you can find cheaper let me know - I need to buy another detector for the garage at some point. See the Aico website for a handy 'what should I fit where?' guide. Hint: Ionisation detectors anywhere near the kitchen are the reason for false alarms from toast etc.
Aico:
https://www.edwardes.co.uk/en/products/aico-ei141rc-240v-ionisation-smoke-alarm---base
Relay base:
https://www.edwardes.co.uk/en/products/aico-ei128r-relay-mounting-base-for-140-160-alarm
As above, the disadvantage of this set up is that unless you're at home you cannot tell which alarm caused the system to trigger - but you can phone a friendly neighbour and say "Hi Bob, I think my smoke alarms are going off, would you mind going and checking that there isn't smoke coming out of the windows?"
One more thing. You cannot mix and match brands and/or models of interconnected alarms. If you go the Aico route then everything must be from Aico (I can't remember if you can mix 140 and 160 devices). You certainly can't start adding Kidde and similar alarms - it won't work and will most probably damage them.