Ah, well, if I've understood correctly what you've now stated, runn3R, that would explain why I could never get my inlet fan to run if I had it connected to Sys Fan 2 header. From system power-on, the internal temperature of my P55-US3L-based PC would have been well below the probable system temperature that would have turned that fan on.
I did try it initially with Smart Fan Control enabled in the BIOS, and also tried both modes, including voltage control, but I was still unsuccessful in getting the fan to run at all. From what you state, even if I were, it'd run at a speed entirely determined by the motherboard, not by me - unless it's somehow controllable via the EasyTune utility or something.
For my purposes - and I guess for a lot of other people's as well - this Sys Fan 2 header connection is all but useless. That's why I now use my inlet fan on the Pwr Fan header instead. As for Smart Fan control, it's a shame that I've had to ditch using that as well. I think that with cooling and quieting requirements as they are now, with PCs, people prefer to have more direct control over the speeds of the fans, rather than leaving it to the motherboard and temperature-sensing. I think that people would rather have all connected fans running from power-on, and so then know that that's the maximum amount of noise the fans are going to make. It would have been very nice if, with Smart Fan control, one could just use the BIOS to set an individual source voltage for each fan, in the range 6v - 12v. Instead, I've had to do it on the three fans I use by my own hardware mod.