@gregjacob I like simple amp circuits. Handmade. Look at Aric audio who has gotten a lot of positive feedback here on audiogon although I have never had the opportunity to hear one.
The amps you listed are all printed circuit board swiss army knives with remotes and lots of features that IMHO mess with the signal path too much. Aric runs wires from component to component and minimizes everything.
But I assume you want multiple inputs and a remote. My system uses the DAC as the "preamp" in that it has volume control and multiple digital inputs. I still need 2 inputs into my amp as I need a pre-in for my HT so I can use the amp to drive the front 2 speakers during HT.
So I recommend figuring out exactly what you need and finding the simplest way to do it. and keep it as simple as you can. Aric will make you an amp with 2 or more inputs if that will allow you to skip the preamp.
BTW, there was a thread recently on preamp vs no preamp and I am in the "no preamp" camp but many prefer a preamp. You can do more damage than good with many preamps so buying a preamp can be challenging. But the right preamp will sound excellent so that is a personal prefernce.
Unless you are killing your ears with concert volumes I feel certain the 300b will be enough power.
I am currently having a custom amp built and can connect you with my builder but it will be a lot more money. given the price range of your new speakers you man be interested. PM me is you are.
Jerry
