I'm a noob. I freely admit it. And I have been ruined by my first higher end combo of headphones, DAC, and AMP. I have gone over to the dark side and will never turn back. I do not have the vocabulary down yet, but I know what I like and the combo of an Audio-GD R2R 11 and HifiMan He-400i are heaven. I purchased an Audio-GD R2R 11 DAC/Amp for work, which I was planning on combining with close backed headphones. Well, I have discovered that I just love the combo with my hifiman HE-400i and Audeze iSine LX IEM, both of which are inappropriate for my office environment. Long story short, the Audio-GC R2R 11 is staying home. Does anyone have a recommendation for an appropriate desktop Amp, DAC, and close backed, over ear headphone combination for someone who has a measurable deficiency in the 4KHz frequency range and a $500 budget? I know these things are subjective, But I discovered the Audio-GD R2R 11 by reading Head-fi. I love the debates and the information gained. Thanks.