My experience is that the sound does warm up a bit as the cabinet gets bigger and wider. Each Omega driver has it's own strengths and weaknesses as do any speakers from any brand. The Alnicos are a bit smoother in much of the range where the RS5 can be a bit whispy. However, I find that in the highs, the opposite can occur. You just have to decide what trade offs you can find acceptable.
You did mention that it happens when you turn it up...you aren't hearing amplifier clipping are you?
I've got RS5's, 8's and Alnicos and I really do enjoy each of them for their unique strengths and prefer any of them to conventional speakers.
I agree 100%. The Alnico driver has fuller midbass to lower midrange than the RS5. The wide baffle of larger speakers or the CAM provide extra lower midrange support. The RS5 has a superior top end. I attribute this to the whizzer of the Alnico driver. Some people can be sensitive to the top end.
At the end of the day, these full range drivers are compromises. In reality, they are wide range midrange drivers that happen to provide great bass and great highs for what they are. IMO, they are best used in a way that reinforces their strengths without trying to make them do mor than they should.
I also have Altec 414’s in 614 cabinets. These 12” Alnico drivers still only go down to about 40-50 hz. No matter how big an enclosure I put them in they will never produce prodigious bass.
For my money, the sweet spot with the Omega line are the single driver models in wide baffle cabinets. The wide baffle reinforces the lower midrange. If I were buying today it would be Super 3 Monitor with wide baffle, Super 3 XRS, or CAM.