The small ombinus is a chromatic voice exchange progression that utilizes the 6/4 figure in the middle for smoothest voice leading:
If we simply focus on the outer voices, we see that it’s the same voice exchange. The inner voices in the harmonies labeled 1-5 simply stay on Re and Fa.
Extending the Small Omnibus
Notice that chord #2 (spelled as a +6/5/3 chord) and chord #5 (spelled as a regular dominant) both sound like a dominant 7/5/3 sonority.
This allows us to reinterpret the last chord (#5) as a new chord #2 and extend the progression.
What key will this lead us to?
Since chord #5 is a minor third below chord #2, reinterpreting as chord #2 will lead us down a minor third.
It also works inverted:
