What's the weak link in my system?

@willemj - I can see that you are definitely a person who is completely reliant on specs and you seem to have the traditional old school opinion that cables do not matter at all. That is perfectly fine. You are perfectly okay to disagree on certain points, but please do not drop down to name calling or insulting people because you do not agree with their points of view. This creates a situation where there is no objective discussion and the thread degrades into a flame war.

Please always try to approach things with an open mind. The traditional engineering approach that states "since a fact is written down as a fact, it is therefore always a fact" is not always correct. We are always discovering new things. Also, the engineer who believes that something is fact may not be able to hear the differences that certain audiophiles can hear.

I took a quick look at your ODAC. I would not say the specs are that great (for a DAC chip). The (now aging) ESS 9018 beats the specs of the ODAC. The ODAC states lowest THD at 0.0015% and DR of >112db. The ESS 9018 THD is 0.0001% (-120db) and DR of 129/135 db. However, this does not necessary mean that the ESS DAC will sound and be superior over your ODAC. There is a lot of missing stuff here such as I/V and LPF audio stages, which will work on further shaping the waveform that is just flat DC voltage injections from the DAC chip. We haven’t even talked about power supply (such as high capacitance, linear power supply filter, cable material, etc.). The ODAC is powered from USB cable, which is a bottleneck and, in most cases, will have a switching power supply from the transport (definitely switching if it is from a common computer).

The ODAC is also designed by NwAvGuy. I’m sure the design is fine, but I have read NwAvGuy’s posting on op amps and I don’t necessarily agree with all his points, especially his statement on the "MYTH" most op amps sound different. I have tested many different op amps in a highly ideal analog circuit. This means a high capacitance (2 x 10,000uf) linear power supply with R-Core transformer, fully discrete Class-A based voltage regulators, very high end electrolytic capacitors with minimal electrical resonance, OCC solid-core chassis wire for power cable, film-on-foil feedback capacitors, etc. etc. In all cases, I can definitely hear differences between op amps. And the specs on an op amp do not necessarily mean they will sound good. You can disagree here if you wish. However, for those of us who can sit down and hear the differences, this is a fact for us that there are differences in different elements.

@jdm11 - there are a lot of different opinions and suggestions posted here.  I do agree with several opinions that your source is very important.  One thing I have found is that if the sound quality or sonic signature of the waveform is not there from the beginning, there is nothing in the middle that will "bring back" that sound quality or refinement.  A $10,000 preamp with a $200 CD player may sound very good, but it is not going to magically "fix" the poor sound quality from the CD player.  That being said, you can spend more and more on a source that you get to a point where you are not able to hear the "differences" between two high priced sources.  One thing that could happen here is that your middle layers (cables / preamp) do not have enough resolution to allow you to hear the differences between sources.

I have taken a look at your equipment list.  Nothing really jumps out at me as a "weak link" because everything on the list is pretty equivalent.  I have absolutely no experience with turntables, so I could not comment on that.  Your Marantz CD 6006 is a fine source.  Marantz has excellent focus on power supply and also its discrete analog stages.  The Marantz equipment is voiced to be on the warm side, so if you like that sonic signature, it's great to stay with the Marantz.  The Parasound P3 looks to be a fine preamp design with good power supply.

As I said, I do not have experience with turntables, so the previous comments that the turntable / phono preamp should be upgrade might be correct.  That being said, I have noticed your PSB T6 speakers are 4 ohm.  Usually, speakers have a drop in their impedance curve where the impedance can reach as low as 2-3 ohms in the bass/midbass area.  This speaker is mostly higher than 4 ohm, but there is a drop to 3 ohm between the 250Hz and 700Hz region:

https://www.stereophile.com/content/psb-image-t6-loudspeaker-measurements

Based on this, I would say that your Parasound A23 amp -might- be somewhat of a weak link here.  If I had your system, I might look at upgrading to the larger Parasound A21 amp.  It has a power supply twice as large.  This may handle that low impedance area in the low midrange better than the A23.  Also, the A21 will just be a much more refined sound than the A23.