It's been a while since I thought this through (so others pls correct me if I'm out)...

If you are using 'direct' then this doesn't use the sub which effectively means your 5200's are in full range mode. 'Trifield' does use the sub, so, if you find that it's lighter in the bass, it's likely to be that the sub and 5200's have not been matched closely enough w.r.t. x-over and levels.

Compare 'direct' and 'stereo' presets for bass weight as 'stereo' brings in the sub (IIRC).

As Chris says above, you can get Trifield to effectively make the centre channel disappear as a point source. For off-centre listening, it's very effective. However, as you also mention above, you can get a very very very good phantom centre from just the L&R. Why would you want to use the centre DSP?

I periodically wrestle with this. I'm currently using L&R only as my G68 is on hols in Huntingdon and it's quite nice hearing the phantom. However, when I was doing trifiled, it was an amzing wall of sound (not in the Phil Spectre sense)

So, it's horses for courses.

Rgds,
Nick