Congratulations on the new preamp. And TBH when it comes to amp and preamp combination - our system matched almost to the T before I upgraded from a Parasound A21 to the Accuphase A-48S. You will be pleasantly surprised by how much the Rhumba responds to tube rolling.
I recently upgraded to an Accuphase amplifier, from the Parasound A21, and this is a huge upgrade in my system. What I am surprised was that - even after I moved from a 250 Watts Parasound to a 50 Watts Accuphase, the "clarift", "harmonics", "drive" and "sense of ease" with the Accuphase is unreal. I keep wondering how can the bass sound so strong with this lower powered amp compared to the previous amp. The Parasound is a fantastic amplifier for the money; but the Accuphase "brings out the realism" and creates "touch me" sound images.
My Accuphase might not work with your speakers as they are lower sensitivity. But there is a used Accuphase on US Audiomart that will pair very well with your Rhumba and will provide you with a nice upgrade.
I you want to understand more on the Accuphase amplifiers, please go through the thread I started - Accuphase amplifier choice.
Good luck and I hope you find and love whatever route you choose - from one Rhumba owner to another!!