I'm all for building your own things but I'm a little hesitant to allow something like Auto-Senses, as it's described as a subsystem, to be as easily obtainable in a simple helmet.
I'm leaning to agree with Cifer that the helmet itself is filled with a lot of fancy gizmos and gubbins that require the complete connected use with the Power Armor. Given the description, it sounds like there's a pretty sophisticated cogitator running. I'm inclined to believe that said cogitator is actually part of the suit itself that also runs the systems of the power muscles, stimulant injectors, etc. At the very least it's very complex being a HUD and all. Also I don't have any sources to back this claim but I have a strong feeling that when disconnected from the suit the helmet doesn't function at all (or any random person could just wear a helmet and run around in it). Vox functions are redundant in the suit's collar, but everything else I think gets "unplugged" from both the power supply and the cogitator.
So what does this mean for players who don't want power armor. Well I have a character with a cybernetic eye, sure it's not nearly as cool or mechanically beneficial as a power armor's helmet. There are pieces of equipment that provide things like night vision and protection from flash grenades, but not all in the same package. Maybe you can get it as long as your helmet has cables dangling from it to connect to a backpack power supply/cogitator or something. seems like a cool look thematically.
How is building a cybernetic eye and implanting it less complicated than making a suped-up helmet? The fact that you can get cybernetic eyes and that fact that photo-visors and preysense goggle require no power source leads me to the conclusion that a good tech could fashion a helmet with a simple display with read-outs and targeting aids without the need for huge back-pack full of batteries and electronics. I agree that it probably has a small battery, maybe you need to recharge it occasionally. Yes, power armour has a huge power pack but that is mostly used to run things that use up lots of power, like the ability to increase someone's Str by 20 points, or the ability to move a 65kg peice of metal as if it weighs nothing. A balistic/manipulator mechanendrite implants have no power source at all(ie, they don't need to be recharged in-game), so I don't see it as a huge stretch.
I'm not suggesting that you take a set of auto-senses off power armour and put them onto a regular helmet (although, I'm sure with enough time and the right tech-use test it could be done), I'm suggesting that you have a helmet custom-built from scratch. Over-lay screens that can be worn like goggles exist today and use up very little power. The cogitator would be smaller and would be more specialized thus reducing its calculations: it doesn't need to stabalize a full set of armour, co-ordinate a users movements, keep a constant diagnostic of dozens of systems ranging from the auto-senses to the waste reclamation system. This would make it much more compact. As I said above the FLUFF indicates that it offers Combat readouts, targeting systems and visual enhancements so I'm not coming out of left feild.
Lastly, the aquisition is at the same difficulty as getting a full suit of power armour. Is it really that unbalanced? In almost every situation it's more advantageous to get a full suit of armour and enjoy its superior protection, bonus to Stregth and 3 sub-systems (including auto--senses).
Oh, just read your 2 last sentances. I'm perfectly fine with the helmet having cables and stuff and a (small) power-pack. In fact I assumed it would be powered in some way. Most gear seems to be powered one way or another, but the game doesn't focus on how often you recharge your auspex or change the batteries in your prey-sense goggles. The exception is Power Armour of course, but as we can all agree, it needs far more power than any one peice of gear.