Is Pre-Amp needed

It's not "needed" if you like what you are hearing. I was doing the same thing but was not happy with the sound. Adding a pre-amp in my system changed the sound that to my ears was an improvement.

this is an endless debate with no answer other than what you prefer...

Right now my preamp sent for upgrading and I use direct DAC /power amp! It works but a bit dry and raw to my ears, a good preamp adds more taste to the sound and I already miss mine. If you want to have analog setup, preamp is a must for volume control.

A preamp can never make the sound more accurate, it can only degrade (it has its own frequency response, THD, etc.), though the degradation is usually not much of an issue for any good one.

Now, volume control and voltage gain are what many pre-amps can provide that many sources need.

However, the Oppo has been measured and shows its digital linearity (for volume control) is excellent, so no worry about worsening S/N as you decrease the volume; it also has more than enough voltage.

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-oppo-udp-205-u...

A preamp can never make the sound more accurate, it can only degrade

This statement is 100% correct. Going direct, has less distortion and colouration, is more transparent and dynamic.
An added preamp preamp, if prefered can only add colourations/distortions as a "band aid fix" for a "source sound" they don’t like.
Get a better source, instead of putting a very expensive bandaid on it. "The best preamp is no preamp."

Cheers George