My Oppo is a bit too bright

The knock on the 105 (I have one) was the power supply. I found Linear Power Supplies on Ebaye. One company provides easy to follow photos. Also replace the OEM IEC . I bought the Furutech with pure silver tail that snaps on the old or new board and a jumper to bypass the 110/220 switch

For ~ $400 you will be amazed

hth

Change cables , Cardas clear reflection excellent balance of 
organic warmer mids and still good detail.

Not sure I’d spend a lot on a 105D such as power supply or the IEC socket but no doubt it will help. I’d recommend using your Oppo as a transport and get a DAC. I have an Oppo 205 and it’s not up to my Cambridge 851C which I was using the DAC in it for my Bluesound Vault 2. I ended up getting a RME ADI 2fs DAC and it is better yet, much better and before I upgraded the power supply on the RME. 

If you’re using your Oppo for two channel only you can probably get enough out of it to pick up better dedicated CD player only like a used Cambridge 851C, or upper used Marantz models. If budget allows keep your Oppo and pick up a DAC.

It will make a good transport. Depending on your budget, the Schiit Dacs have a good rep as does the Denafrips Ares II at around $700.
Your coax cable makes a difference. The mellowest coax digital cable I've found is the Audio Advisor Penangea for $95. Belden's standard coax at $20 is also a good cable. I've tried the expensive cables and you can expect more detail but attendant brightness and more of what you don't like. 
Also Have you done the latest Firmware update on your Oppo. They still have a legacy web site and can upgrade your unit They sent me a DVD to upgrade my Oppo 93 software. 

I have several CD players but I use my Oppo 105D more than the others mainly for the features available via the remote, like volume. Also, it has a solid, competent sound. I bought a Benchmark DAC1 many years ago, but never got around to using it until I bought a pair of Audeze LCD-X, closed back phones. When I hooked up the DAC to my Oppo, I was shocked at how much it improved the sound. I shouldn’t be surprised as the Oppo cost around $1400, and handles nearly every type of disc, while the Benchmark cost $999 and simply converts the digital signal, but does it very well. Forget that crude comparison and just believe me that a good DAC (like Benchmark) will tame that bright sound of your Oppo.