First thing, halfway on the volume pot is about 20dB lower than all the way - that's 1/100th of the power. Do not be afraid of using the upper half of the volume control! You paid for it, might as well use it... :^)
(By the way, I assume the voltage checks are OK - no serious problems with the Seduction operating conditions. Just making sure.)
Second - "congested" is a good description of what I hear while gear (mostly capacitors and transformers) is breaking in. If you don't have at least 50 hours on the newest component, try to suspend judgement until you do. I didn't believe in this effect - it makes no technical sense - until I did the experiment of doing the breakin without listening (driving a resistor instead of speakers). I heard exactly the same change that I had heard while listening to the process. And I'm a reasonably hard-headed engineer.
Now to the gain issue. I do have a white paper on the Bottlehead Community page on signals and noise - bottom line, signal levels are far from standardized in home audio gear. So it's not surprising that one source (phono) may be a lot different than another (CD player). iPods, tuners, and internet/satellite radio are other sources with their own signal level peculiarities. We can make changes to accommodate these differences but I'll put put off that discussion until we make sure there is nothing fundamentally wrong with your components.
So - first questions, what is the output level of your CD player, and what is the output of your phono cartridge? If you can't find specifications for these, give us the model numbers and the community can often locate the missing information.
Second question, what kind of music are you listening to - I ask this one just because the compression used in the studio varies a lot between genres and that can make a big difference.
Third question, does the vinyl sound like the equalization is OK - no seriously missing or overemphasized bass, treble, or midrange? The makes sure that there is no error in the equalization network of the Seduction.