So, I have been composing this "Requiem for String Quartet" on and off for a few weeks now. I call it a Requiem because of its dramatic arc through lamenting melancholy, painful harshness, solemn peace, and a majestic feel. And to reinforce the fact that it is a Requiem, I have been using the Gregorian chant "Dies Irae" as a melodic basis for quite a bit of the piece. I have however been treating it differently in different parts, some parts more contrapuntal and others more solo. Some parts, I wrote the melody as close as possible to the chant and others I took some liberties with, but kept the overall direction the same. And I'm at the point where the chant goes from the Tuba Mirum to the Rex Tremendae. I intend to treat the melody in yet another way here in the Rex Tremendae, having the strings in a rhythmic unison, giving a sort of chorale harmonization of the melody.
I'm currently in the key of Ab major and I'm wanting to modulate to D major. I figured, since I have 2 question phrases followed by an answer phrase, I could do 3 little tonicizations instead of 1 big modulation without tonicizations. So like I would go from Ab major to a second key, keeping things quieter and maybe having the last chord of the phrase, the dominant seventh be staccato. Then I would go from that second key to a third key, again quiet and possibly ending staccato. Then I would go from that third key to D major, with a confirmatory crescendo.
So basically, I would be after something like this harmonically:
Pre-Modulatory Phrase | Phrase 1 | Phrase 2 | Phrase 3 | Post-Modulatory Phrase
Ab:I -> chords -> V7 -> I -> Sec. Dom.
1: V7 -> I -> Sec. Dom.
2: V7 -> I -> chords -> V7/D
D: V7 -> I -> chords
And I put numbers 1 and 2 for the keys that I don't know yet because I couldn't really use letters, or it would look like I decided on the keys when I haven't. Anyway, the distance that I have to modulate is the largest distance I could possibly modulate, the tritone axis. This makes things a bit tricky if I don't want to use the very quick diminished seventh modulation(which I'm not wanting to do here) or the Tritone Substitution(I think it will sound too abrupt to use Eb7 as a Tritone Substitution after all the material that has come before in F minor, C minor, and Ab major).
Is it even possible to string 3 dominant seventh resolutions across a tritone axis to get this smooth modulation via 3 tonicizations? If so, is there more than one possibility or is there just 1?