Sound quality is highly subjective and varies from individual to individual. Comparing a reproduced sound to a reference (i.e., live music) is the best anyone can hope for when it comes to subjective reasoning.
The OP indicated he did not expect a difference when using HDMI yet he claims he did. Who are we to tell him what he did or didn't hear without being present while the listening was actually taking place? Unless anyone was there to witness the event, any argument against his claim is pure speculation, but speculation based on experience and knowledge we already possess.
Bull&hit or not is anybody's guess without listening for themselves.
I can't argue with the Engineering aspect regarding the digital signal. I would not expect to hear any difference either. I just prefer to reserve judgement until such time that I can hear it for myself.
Naysayers are in abundance whenever anyone makes a claim that rocks the boat. Just think where we'd be if everytime someone discovered something new they listened to the negativity that invariably ensued. We'd still be in the dark ages.
To the OP - If you found a product that enhances your enjoyment, good for you. Whether it actually works is anyone's guess. The fact that you perceive it to work is all that should matter to you. Enjoy!