not sure exactly what you mean by addition digital ins on word clock... the AES inputs are on DB25 and have SRC, so do not necessarily need to be locked to clock. You only have 8 recording tracks, period. What you can do is combine as many inputs as you want onto a recording track though, so you could for example record mic 1 and line 1 on track 1, then use the gain pots to mix the 2 inputs (or more) to a single recording track. The digital inputs can also be combined with analog inputs, but obviously there is no gain pot for the digital inputs, so gain can't be adjusted nor can they be muted on the Cantar while rolling.
One thing to note, you do not have to assign the mix track to a record track for it to be active. So for example, you could assign digital 1 to 6 to tracks 1 to 6, then mic 1 to track 7 and mic 2 to track 8. The only problem is that you would never be able to bring tracks 7 and 8 into the mix unless you are using the Cantarem which has 8 faders (other than mixing with the trims). There are digital direct outputs of the first 6 recording tracks as well as an assignable digital output. For analog outputs there is a balanced output on XLR5 and a foldback output on unbalanced TA3. Any of the outputs, wether digital or analog, can be assigned to the mix output OR can be a matrix output of some sort (including inputs that are not being recorded, if you want a communications feed for example). So in this way you could record 8 ISOs, then send the output to a 2-track recorder to record the mix. In my case I have a Zaxcom IFB200 hooked up to the AES output and in this way could record 8 ISOs and deliver a separately recorded 2 channel mix if it was really necessary, but generally use the Cantar on jobs where 6 sources cover it.
I own the Cantar, love it, don't want to replace it with anything else, but when it comes to the Cantar, I think logic dictates that I would never really recommend it to anyone else. You have to know why you want to use it and not be talked out of using it by common sense. From a value perspective, it just never really makes sense, unless you are getting a really good deal on it. I like that I can take it into the rain. I can honestly say it is the most reliable recorder I've used, beating out every Sound Devices or Zaxcom unit I've driven... not to say I think those are unreliable, just statistically, the % failure rate I've had with the Cantar is lower - but not zero. Shit happens, even to Cantar. I like that it is impossible to wash out the meters with sunlight. I mean literally impossible - you can try, but with the sun in our solar system on the planet earth, you can't do it, you'll blind yourself before the meters are not readable. I like that there is a menu system that allows lots of flexibility, but once your rolling, the things that you would want to adjust while rolling, are done with tactile buttons, faders, and pots. You can adjust this by touch and don't need to read a screen, unless you are adjusting limiter or filter parameters (or panning - panning in ENG/reality situations is not easy with Cantar - I do it myself, as I work a fair amount of unscripted, but you have to become adept at holding a boom pole, while pressing a button with a pinky, and then spinning an encoder with your other hand). Nothing with the Cantar was really designed with "plain logic". Shit is confusing sometimes. I still have to break out the manual occasionally when doing something I haven't done before or done in awhile. Its very "French" I guess, not being an expert on the French. I can say, though, after years of using it, that I develop a muscle memory and I personally find the operation very easy. Its just the first time you try to turn it on, you can't. you look at the manual, figure it out, then after practicing for awhile, it becomes second nature. Same thing goes with pretty much every other function of the unit. I would compare it to flying an airplane versus driving a car. The average person can't jump into a cockpit, figure out how to start the motor and do all the other pre-flight stuff - but after training and experience, you become expert on it, and if you need to do some sort of emergency maneuver, good training and experience will pay off. Pretty much anybody with any level of training can jump into any car and figure out how to get going. I'd say that is the Sound Devices approach. There's something to be said for that approach, but if you go Cantar, throw out any ideas of it being a "logical" journey.
by the way, as far as updating for modern age, one thing I did was forget the idea of accessing the HDD via 6-pin firewire and replaced the internal HDD with a PATA CF card reader. I then put a 128GB SanDisk CF card in it, formatted for 120GB (Cantar won't recognize more). This has been 100% reliable for me and if I ever needed to replace with main volume, its just a card swap away. Sometimes when I need to backup content to my main storage RAID, I pull the main card and just use a card reader, rather than the antique firewire connection. I have also purchased an IDE to CFAST caddy. I haven't bother to try to install it, but the logic is that if there was some reason for me to go CFAST, I could - haven't seen that reason yet. DVDRAM is obviously worthless today. If you do buy a unit, make sure it has the CF removable media bay OR you know where to buy one... as that is the card you will deliver on a daily basis.