I am not an expert on these, but,
I am not sure you can "back off" from 16 heads, all the way to 2
As you increase the number of heads, I would think the machine overwrites firmware, juggles memory addresses, etc, changes encoding.
While the engineers anticipated UPGRADES & allowed an upgrade path, I don't know that they were greatly concerned with DOWNGRADE path. It might be necessary to replace a formatter board or whatever holds the firmware.
If I thought it was that simple, I would have the box truck warming up already (nobody is more fearless about starting a project that might be above his skill level than I am)
We have a CET Q5 (Paid 20K For it, in good working condition... We looked it up and the next closest in price was 45-50k, so it was a steal) - It started with 4 heads, 2 werent that great...ran it for a few years, all on original heads - finally we decided to upgrade, bought 2 heads and just installed them last week... now it's printing great, all from youtube videos CET put out themselves.
CET is very user replaceable, they design it around the users doing all the repairs - They even have courses that teach you to be a "Tech" for free every once in awhile. Covid put a wrench in it, so we're awaiting for them to open it up - But their system is SO much more open than any other system we used... it's refreshing.
I've never seen a 16 head... I believe ours fits 8 heads. But on our machine you can select the head configuration in a drop down menu. CET is very open and will send you upgraded firmware / BIOS through E-mail if you ask, so if it is some custom firmare... I don't see why they wouldn't send you the original to flash it back to 8 heads.
If its been sitting in storage for years and needs all new heads... I'm going to guess the ink lines werent flushed though. Not a biggy... it's $20 for 50 FT of the line, so for under $100 you can re-run them all. Easy access underneath the machine... But It's like running Cat cable... "Easy" but a pain in the ass when you're crawling through such tight spaces! And I'm sure a slew of other things would need to be changed if it werent properly put into storage mode. But its honestly one of the easiest / user friendly printers I've found for repairs - We havent taken the course and we've reached out a few times and theyve sent detailed instructions on what the problem is, and how to fix it every time. Usually it's due to lack of training since we bought the printer used... but theyve done quite a bit of support for us, even though we dont even use CET ink and we use vanguard ink instead. It's a great company, and if I were to buy a new flatbed, I dont think I'd buy from anyone else!