Couple of things, yes led diodes lose intensity over time. Rapidly if not cooled well.
A "blown channel" can just be a open diode on the string.. You have 27 or 28 diodes in series (55 total). One "open" can cause an entire string to die. Depends on the design though.
Not sure about the wifi thing and different drivers. Probably also model/year dependent.
There are some substitute drivers you can find but with err "issues" mA may not match but close. May not have the 12V for the fans and/or different dimming protocol.
Actually the dimming thing may cause the wifi vs non-wifi driver difference.
Overall sounds in your case possible multiple issues and a lot of diode replacements.
Simplest thing is to swap the drivers and see if the channels respond the same or differently.
Like if you swap the driver running the "dead" channel to the dim channel and the dim channel isn't dead, it is not the driver..
Now there is one place that carried drivers (and sbreef does for their lights (generally same drivers)) but off hand my memory failed me. Besides it still could be for a different "black box"
70-100v 480mA That is the led driver.And driver w/ those specs (or close) will work.
More mA brighter diodes, less err less.
Does need the high end voltage.. Too little upper end either string won't light or it will be dimmer.
You have a power supply in there (12v ps) for the fans.
The other driver (15-19v 300mA???) not sure what that is for.
Now doing some guesstimates here
28 diodes @ 3.2v = 89.6V
Soo replacement driver really needs to fit the upper end (100v) Lower end is of little concern.
Honestly, it doesn't seem worthwhile really over buying a new one.
As an example:
LCM-40U:
Matches the upper end voltage but current reduced to 350mA which, at best leaves you w/ a 35watt channel.
LCM-60U:
Less upper end voltage and it would (should?) light the string but not guaranteed to run it at it's 100%. Depends on the V(f) of the diodes. Next it overdrives the diodes from the orig. driver at 500mA. 500w at max voltage.
Close enough though.
Dimming is 0-10v dc. Probably best on a wall timer as well.
It's a little complicated doing substutions.
Why your orig driver states 70 Watts is an ?? to me
W = VxA so at best .480A X 100V (max) is 48W
Your MODEL/Brand would possibly help.