Thank you so much for your response.
First off, I received the TEAC UD-H01 today. Setup was quite easy, as all that I really had to do was download the driver for the DAC, connect the power cable, and connect the UD-H01 to my PC via... USB.
First off, I played music at 192kbps quality. The improvement in detail was quite noticeable, however, the range of sound available seemed to not be as wide as what I expected. The frequencies at either ends of the spectrum seemed to drop off. That being said, the sound that was there, was quite detailed. There was an immediate "accuracy", for lack of a more accurate word, present. Instruments started to sound more like how they do in real life, and I am still amazed at how much I really have been missing out on.
Before, the different instruments sounded like they were muddled together. There was no defined beginning or end to the different instruments. The defined sources of the sounds were also quite unrefined.
Now?! Well, how do I go about this?
I have owned my HD650 for over 6 years, and I have just now begun to understand just what I may have possibly invested in all those years ago.
Switching over to 256kbps, the sound may have improved, and perhaps listening to it over and over, then switching back to 192kbps, I may hear real difference. I am sure it's there.
There is a long story about why I didn't have a PC for the last 5 years, but prior to my last PC malfunctioning, I had ripped approximately fifty albums from .wav to .flac. Since I switched hard drives into my new PC, I downloaded the extension for Windows Media Player to be able to play FLAC files. Moments later, and I must say that I am now corrupt with this most extraordinary experience. What seems to be every detail to the sound is present in the most intricate display of instruments and vocals. They sound as if I am sitting in the front row of a very intimate concert. The sound stage could be just a bit wider, but is the most accurate I have ever experienced through any headphones.
Every instrument seems to be there in its entirety. No more clashing of "like" frequencies. Every piece of the music is dissected, yet presented in the way that it is fused together with only the slightest thread of composition. Together, the notes of music enter the ears without any particular authority, in that they don't force me to accept them how I have been, rather, it seems more of a rescue. A truly blissful rescue!
The UD-H01 seems to drive the HD650 well enough, however, I'm not very satisfied with the weak bass with the .mp3 files. I believe all it took for me to become jaded was to hear my first .flac track through the UD-H01. It's going to be extremely difficult to not listen to the HD650 without a DAC now.
The Onkyo A5VL shows up on Monday, and I believe once I receive it, I will send the UD-H01 back as I know that compared to the UD-H01, the A5VL is a better unit. I have also ordered the Audio-GD NFB-5.2, and will try it out.
As far as my reservations about using USB as an input, there are times when there are a lot of issues with syncing, from what I can guess. What I am talking about is when I go from one folder to another to play a track directly from my hard drive, I sometimes hear scratching noises, or clicking. It's definitely not prevalent/consistent, but intermittently comes about. I plan on going out and getting an S/PDIF cable so I can compare if there is a change.
Once again, thank you for your input, and I am very much looking forward to what is coming my way in the next few weeks, as I decide on what I ultimately want to use. Looking forward to hearing the cymbal reverberations, and the guitar strings vibrating on the pick for that fraction of a second.