Pairing B&W 804S with Power amp

Get a tube pre and be done with it

i think you can try out with a regular pre amphttps://xapkinstaller.xyz/

A used McIntosh tube preamp and solid state power amp will fit your budget and will also be a good match with the B&Ws. 

Thanks for all the info.  Looking at McIntosh MC-312 power amp and C8 Tube pre-amp.  Any thoughts?

I have a Rotel RB-1072 I used a long time ago on a pair of B&W 703s. Now I use it as a rear channel amp in my surround sound system. I also own a McIntosh MC462. 
When I was between amps (benchmark and McIntosh) I used the Rotel for a few months again on a pair of Thiel 2.4. 
What you will get going from a Rotel power amp to McIntosh is a more relaxed sound. All the details will still be there but it will be as if the rough edges are removed. The Rotel amp is a little hot on top too so you might see some tonal balance change. All in all I really like the McIntosh and feel it is worth upgrading over the Rotel. With the mc462 I find myself listening to class rock and hard rock albums I would never listen to on the Rotel while audiophile stuff sounds just as good as ever. 
Your preamp might effect your sound more than the amp. Make sure you demo tube preamps before buying one. I am not a huge fan and have owned a few. But the 804s are pretty bright and harsh IMO so maybe the tubes will help if that is what you are trying to correct.