Well, I think I have sort of found my answer. Avenza Maps is an iOS app that seems to be considered one of the best for handling the above mentioned map formats. While the App is free, the downside is that it has a $49.99 annual subscription fee in order to enable the Import feature so not planning to take that route. There are other free/cheap ones but they don't look overly great...
However of particular note is that in the built in Map Store they resell the TASMAP eMaps for cheaper than TASMAP ($1.49 vs $2.00 so not much in it) - the listed publisher is 'nswtopo'. The downside to this method vs purchasing direct from TASMAP is that it is stuck to be used within their app program (i.e. can't be shared with other people/programs etc). They also don't offer all of the TASMAP maps - only the 1:25,000 range (which has been superseded by an updated 1:50,000 range - but in my comparison I think that the old ones might have been better and the new ones may have actually had details intentionally removed). One of the things I really like is that you can preview the particular maps in full detail on your computer at maps.thelist.tas.gov.au
Today I have played with/tested the Avenza app with free maps and find the iOS program to be good. I've bought 13 of the the 1:25,000 maps for an area that I plan to visit later this month on a 4WD/camping trip with mates and will test it out then to see if I have a new favourite off road navigation app. I've found the big name providers (MudMaps, MemoryMap, VMS, Hema, ExploreOz Traveler) to be very limited in detail for Tasmania so I'm hopeful this will be better.
My biggest complaint with the operation of Avenza is that each map is individual. So you can't scroll from one to the next fluidly (e.g. as you do on Google maps of the List website), you need to load the next one up and view each in isolation.
The other option is HEMA Explorer iOS app which when upgraded to the Pro can access the Tasmania TheList maps. Cost of this is $9.99 per month or around $50.00 annually. I have tested it today following purchasing a months subscription and found it's offline use to be terrible (I downloaded the map data to the device prior to disconnecting and found it's rendering to be patchy and sometimes non-existant and merging maps). Wouldn't recommend this option unless you are will be in cellular data reception continuously.

