From a 2-count on singles (floaty ones), A throws a double (instead of the single; in red in the diagram) to B. A then makes a last self before going into ultimate with diagonal throws. B waits for the double to come down before getting into ultimate with tramline passes by throwing a left hand passes (in blue) under the incoming doubles.
2-count to ultimate
From ultimate on singles, the juggler who is throwing diagonal passes makes
a diagonal double (LH to LH) instead of a single, followed by a tramline double
(RH to LH) before clicking into the 2-count. When the first double arrives,
the other juggler goes directly into a 2-count (a self instead of a pass, you'd
better react quickly!).
The 2-count you both fall into can be juggled on singles or doubles.
ultimate to 2-count
I've also found these two variations (from ultimate to 2-count) while drawing the diagram of the transition above.