Thoughts on using the DAC in my oppo 205 with a CD Transport.

You are using the dac inside the Oppo when you’re playing cds. It wouldn’t make a difference or at least wouldn’t give you what you’re looking for sonically if you use audiolab or any other transport to feed the Oppo. You need an external good quality DAC and feed it using Oppo as a transport. That’s a quicker and surer way to get to where you want to be. 

In an opposition to your scenario. I have an Oppo 105 that I use as a transport with a Chord Hugo TT II as the DAC and have had very good results. The Hugo definitely outperforms the Oppo DAC. But in reality I seldom play CDs anymore with most of my library available on Qobuz

As "audiophile1" eluded to, it's all about the DAC!!!  If I were you, I would definitely explore the vast and wonderful world of external DACs for the absolute best digital sound.  A few years ago, I invested heavily in acquiring a top-notch external streaming DAC for streaming Qobuz via Roon, and in over 30 years in the hobby, I've never been happier.  Also, I would toss the Oppo altogether and use something else of an even higher quality as a transport (as you mentioned) to mate with the upgraded external DAC.  "Now you're talkin!!!"  Happy listening.       

I agree with audphile1, and at a later date when finances are there upgrade to a better transport. I was in your exact position years ago and found that a dedicated Dac and transport there was a big improvement.