@jrpnde it may help to know if you're specifically looking for the OPPO sound character and also if you specifically want to use the analog outputs on a CD player instead of an outboard DAC (second box). From your question, I think it's safe to assume you do not want to use the DAC in some existing equipment you own? But you are asking if anyone is unsatisfied with how OPPO sounds.
OPPO used the flagship (at whatever time the product was being designed) ESS Sabre DACs with a design goal towards neutral, accurate and precise sound. I can't think of a CD player with analog outputs that uses ESS and is designed with that goal in mind, off the top of my head. But there are several DACs that do, which you could then pair with a relatively inexpensive but high-quality transport.
As for the sound of OPPO—it's very much a preference. I would characterize the ESS sound as a bit more punchy and exciting than AKM449X-based DACs, for example. You may have read complaints online about ESS sounding a little harsh in the treble—that may or may not apply to you as many other people are obviously very happy.
In any event, I don't think buying a used OPPO would be a bad choice.