Key Change

Working on a small piece for string quartet + flute that modulates from Ab Major to B Major. It's a medley of two songs...the first song ends on the pitch Ab, and the 2nd starts on D#(Eb). 1st song is in Ab, and the 2nd is in B Major

What is a lush progression that will modulate between the two keys?

I'm more of a voice-leading kinda gal, but I came up with this on the fly. I have no idea if it works in the context of your own work, but in general, I'd advise starting with moving lines that mesh well, then filling in gaps. Happy accidents happen all the time!

Another way would be to move to Abmin for a moment and then, from there, to its parallel major of Cbmaj (enharmonically equivalent to Bmaj). I think it could be quite smooth specially if you go through the V64 --> V progression (B/F# --> F#).

For example: 


I guess this couldn't be considered a lush progression, though. As @Monarcheon suggested, for a lush progression it might be better to start with some line (maybe melody, or a strong bassline that you know points towards B major, or both) and start filling in the remaining voices in any way that sounds good.