If your OMEX is set up similarly to mine you won't have a MAF sensor and it works on a speed density principle rather than the OEM mass air flow principle.
Mine is set up such that the feed back loop maintains stoichiometric AFR up to 3500 rpm or half throttle, whichever comes in first.
Over those parameters, the ECU mapping takes over and runs richer according to a dyno developed map to get maximum performance.
The OEM ECU uses the MAF sensor to calculate the amount of air going into the engine and will therefore compensate to some degree for a less restrictive filter up to a point. The problem is that the MAF sensor itself is restrictive and will only work within certain parameters. Beyond that it can't compensate and it will run lean. (and probably throw up a warning light)
The problem with the MAF system is that you are stuck with whatever AFR the OEM chooses and that will probably be biased more towards fuel economy rather than power unless you get the OEM ECU re-flashed.
Because you have individual throttle bodies, you can't run a MAF system hence the change to the speed density type stand alone ECU's such as OMEX.
I changed to OMEX so that I could have control of the fuel and ignition map as I made modifications to the engine.
One problem of oiled filters is that they can contaminate the MAF sensor and then the ECU will get false readings. K&N dispute that by the way.
Exactly. One of the main reasons that I changed is because the standard intake system could not be adapted to the sports exhaust fitted by Aero Racing from new. At that time there were no readily available re-flashes of the OEM ECU. With the throttle bodies and Omex ECU I was able to adjust all the engine parameters to get optimum results. Some work was done on a rolling road starting with Omex's base calibration but the final tweaking I have done using recorded logs on a portable PC. A challenge and great fun.