Should I eliminate my preamp?

This is a very smart move, unless you need any of the facilities offered by the pre amp, such as a phono input , the option to switch between multiple inputs, or tone control. But for a basic system with just a disc player and perhaps (if your Oppo alllows) an optical input for e.g. a television and/or Chromecast Audio this is fine.
I do effectively the same in my home office system: computer as source, into an ODAC usb DAC, into an Emotiva Control Freak volume control, into a Quad 405- power amplifer. It works like a treat. Adding an extra link in the chain can only degenerate the signal.
Pre amplifiers were unavoidable in the old days, because various sources had pretty divergent output levels, and in particular the turntable, that needed RIAA equalization as well. These days the 2.0 volt cd redbook output standard for rca has been adopted by quite a few other sources like many DACs. As it so happens, that is also a common input sensitivity for many power amplifiers (double this for balanced).

Since you already have the components, listen with your own ears. For me, I prefer having my Oppo 105D going into a processor or preamp and then into the amp. That sounds better to my ears but possibly not for yours.

(((This is a very smart move)))
 I strongly disagree......
((( Adding an extra link in the chain can only degenerate the signal. ))))
If your listening to a preamp with 55 cents integrated circuits you may be right
At first, it may seem cleaner with elevator music yet try it on something with
dynamics. As Mcgal suggested try it yourself and listen.
 You may have also discovered you need new tubes or different brand type installed.
 What is model pre amp it?
 Best JohnnyR