Without looking at the score, here's my guess:
Let's say you have an experimental song where there are two main lines playing in 2/4. They both start at the same time, but one of them has a one beat pick-up while the other doesn't. Both lines change chords every two beats.
The chord progression might be written like this:
Line 1: C Maj | F Maj F Maj | A Min A Min | C Maj Line 2: C Maj C Maj | E Min E Min | C Maj C Maj
So now we have a situation where a chord in one line is dissonant with the other line for one beat, but consonant the next beat. For example, the E minor chord in the second line will be very dissonant with the F major chord it comes in on, but consonant with the A minor chord the first line transitions to.
My guess is that the two sections of the song in different tempos have a similar relationship in "On The Way Home To Earth." McLaughlin may have deliberately written the chords the orchestra plays so that they are consonant with the faster rock group at times and dissonant at others. The fact that they play at different tempos allows this tension to be especially complex.
EDIT: I just listened to the piece. It sounds like in addition to what I wrote above, you can interpret the rock section and the orchestral section independently. The rock section has its tension and releases, as does the orchestral section. Since the orchestral section is so much slower, though, it has more sway on whether the song is consonant or dissonant. Even as the rock section quickly builds and releases tension, if the orchestral section is playing a dissonant chord, the entire piece sounds tense at that moment and won't release that tension until the orchestral section resolves.