"I didn't know Onkyo made a multi-channel amplifier. Is it an older model?"
I was joking about my equipment! I think that segues about the other gear distracts from the point being made. I believe that Meridian is a "purist" company, and that some of the things they do to make the music sound more pleasurable are questionable. Turn off your surround sound modes, upsampling and other DSP processes using a good recording and compare for yourself.
Have you heard a Meridian system with 3 identical front speakers playing Trifield?
If so, what model?
We will not kill you because you have a non-Meridian system :p, so you don't have to fake your system for us..
I think Trifield comes to it's own with 3 identical front speakers. When you put a lesser speaker in the middle it might loose out to Direct mode. Because of powerhandling difference and full range capability. As is the case imho when having DSP8000 and DSP5200HC and driving them harder, on medium volumes it works and you have more clarity in voice etc, but yes the soundstage will be a bit different. In many ways it's easier for the brain to get the soundstage sometimes on Trifield. I don't know why but I have heard it on several recordings.
Until I get a more power handling center I will primarily listen in Direct..
What center are you using? Is it identical to your mains?