You should be able to use either, but you will need to use the configuration program (envy24control) to change the clock source from internal to word clock or from internal to S/PDIF on the second interface. You may have to install the alsa-utils package to get the envy24control program if it is not installed on your system already.
Connect the appropriate cable between the two devices, make sure to set one device to internal clock, connect the cable to the output of that interface, connect the cable to the input of the device using word clock or S/PDIF clock.
I have never had two of the same type of card installed in a computer, so I do not know how the two different cards will be identified so that you can make sure you are setting the appropriate device to external clock. See below.
You will need to start jackd using the primary card, then start zita-a2j for the recording side and also zita-j2a for the playback side. should be something like (not exactly, see notes below):
zita-a2j -S -d HW:M1010LT-2 -r 44100 -c 8
zita-j2a -S -d HW:M1010LT-2 -r 44100 -c 8
Note that I just made a guess for “M101LT0-2”, and assumed that if the cards are usually called M1010LT then there would be something to distinguish the first card from the second. I do not know how the two cards will actually be named. Look in /proc/asound/cards and see what names are there in the [ ] bracket characters.
The -r argument is of course the sample rate, it will need to match what you set for the primary card, and you will have to change it if you change the sample rate of the main card.
The -c argument sets the number of channels to use, I assumed 8, but I think maybe you can use 10 if you want the 8 analog inputs and the S/PDIF also.
Note that you can run the cards without synchronizing the clocks by removing the “-S” argument for the zita programs, but in that case it will cause the audio to be sample rate converted to account for the very slight mismatch in sample rates when using unsynchronized clocking devices in two cards. Assuming you can find the correct place to change the clock configuration there should be a slight theoretical advantage to synchronizing the card clocks. Whether that is audible enough to be worth the effort of connecting and configuring the two cards you will have to decide for yourself.
If you want to try running without synchronizing you still need to check /proc/asound/cards to find the correct names, but then with no configuration changes to the cards you can start jackd using the first card, then load the zita programs:
zita-a2j -d HW:M1010LT-2 -r 44100 -c 8
zita-j2a -d HW:M1010LT-2 -r 44100 -c 8
Whether the cards are synchronized or not, loading zita-a2j and zita-j2a will cause new devices named zita-a2j and zita-j2a to show up in the jack ports list, you can use the connections window of qjackcontrol to connect them just like the primary card which shows up as “system” .
If that works and you like to use the two card configuration always, you can have qjackcontrol start the zita programs for you automatically. In the Options tab of QJackcontrol check the box for execute script after startup, and put the two commands into that box with a ; character separating the two programs, and a & character after the end. The ; separates two commands so that they can be distinguished from one long command, and the & character means keep running after starting a program, do not wait for it to finish before going to the next task. So in the execute script after startup box you would put something like:
zita-a2j -d HW:M1010LT-2 -r 44100 -c 8; zita-j2a -d HW:M1010LT-2 -r 44100 -c 8 &
Then in the execute script on shutdown you can put this to stop the zita programs:
killall zita-a2j; killall zita-j2a
I do not have two of these cards myself, so some of the information I am having to make my best guess based on how it should work, but if you get stuck you can post back here and someone should be able to help.