Hmmm... as long as the Knight was 0-1, an HQ and expensive as heck, then maybe.... I really like those Magos HQs though.
I did a bit of digging around on Lexicanum, found a few things that might be helpful:
Ranks of the Adeptus Mechanicus
* The Ruling Priesthood (Techpriests):
* The Ordinary Priesthood (Techpriests):
o Rune Priest
Divisions of the Skitarii
* Hyspasists (infantry)
* Sagitarii (heavy weapons)
* Balisteria (artillery, vehicular)
* Cataphractii (armored vehicles)
* Praetorians (Obliterator-like Servitors)
* Tribunes (officers)
Legio Cybernetica Robot Types
* Crusader (light, agile, anti-personnel)
* Colossus (siege)
* Cataphract (multi-purpose)
* Castellan (siege and anti-tank)
* Conquerer (assault and anti-tank).
Here's an idea I had after reading your Magos Cybernetica. What if there was a base Skitarii guardsman-like troop, but also a troop choice only available if you have the appropriate Magos HQ? Not only would it help to make AdMech armies very different from each other, but it would also help to limit Knights as HQ options while still keeping them available--after all, if you use a Knight as your only HQ, you only have one Troop option.
I also came up with a few special rules as well:
Emotionless: Many Tech-Guard soldiers have undergone emotional-suppression surgery in order to be more disciplined in battle. This makes them feel no fear, but also no aggression. Models with this special rule are Fearless, but do not recieve the usual +1 Attack for assaulting. (this would be an upgrade option for everything in the army that's actually Skitarii, i.e. not tech-priests or robots)
The soldiers of the Skitarii more often than not have at least some level of bionic augmentation. This will be listed as "Bionics #" with the number representing the level of augmentation. These levels are cumulative, for example a model with "Bionics 3" would have the benefits of level 1, 2 and 3.
Some of the basic troops, probably with Guardsman stats, would maybe be at Bionics 1, upgradable to 2 at a fairly low cost. Anything beyond that would be Elite, Heavy, Fast or HQ.
At this stage, a soldier may have some small mechanical body parts or organs that are far more durable than the original biological part. The model recieves a 6+ Invulnerable save. They also recieve +1 to their Toughness, similar to how the bonus from bikes work (so the model is still treated as its base value for calculating Instant Death.)
The soldier recieves sensory augmentation in addition to its bodily enhancements. This model has Acute Senses, and treats all its ranged weaponry as twin-linked.
With further bodily enhancements, this model's armor save increases to 3+, and it recieves a shoulder-mounted gun controlled by a Mind Impulse Unit. This gun is fired in addition to the model's normal weaponry, does not count against the number of ranged attacks it may normally make, does not benefit from Bionics 2's twin-linking bonus, and the model may assault after firing a Rapid Fire weapon. By default this weapon is a lasgun, but if they have any options for replacing their standard weaponry with alternative ranged weapons, any of those may replace this lasgun instead.
After even more enhancements to its muscles and bones, this model's invulnerable save increases to 5+, and it recieves a +1 bonus to Strength that is added after any multipliers (such as power fists) are applied. In addition, it recieves upgraded sensory implants that allow it to, once at the beginning of your turn, measure the distance from this model to a single enemy or terrain feature. You are not required to fire or assault this enemy if they are the target of this measurement.
Now much more machine than man, this model is now equiped with a basic self-repair system that, while not perfect, can sometimes return the soldier to a partially functioning state. They recieve the We'll Be Back rule as if they were a Necron, although after they return for the first time they treat open ground and roads as difficult terrain. If part of a unit, they will not leave their comrad behind, and are all subject to the associated movement penalty.