System upgrade advice

Vjb, It would be helpful to know what interconnects and speaker cables you are using. Possibily changing interconnects or speaker cables could tame the high end shrillness.

I find the B & W speakers as bright as the Paradigm's.

I doubt you will outclass those electronics with those 804's, but I would audition them first. If you can find a dealer to loan them to you, that would be best.

I like the Paradigm Studio series, but can see where some can find the tweeters subjectively "hot". Speakers should be where you spend the most time/money getting your system to sound the way you think it should.

"I'm considering replacing them with maybe some used speakers around $2.5k (pair) like some B&W 804s."

You'll make the problem worse doing that. Also, you're not going to solve the problem by just going out and buying something new. The whole system contributes to the problem you are having. You need to have some type of plan or goal as to where you need to end up, or you'll spend a lot of money and not fix anything.

Looking at your system, I suspect the problem may be shared between the tweeter in your speakers and you preamp. But just remember, anyone who hasn't listened to your system first hand, is guessing. You can start by connecting your CD player directly to your amp and use the volume control that Oppo gives you. Play some CD's that are giving you the most problems, and see if things get better, or worse. That will give you an idea as to what you need to do.