Thats because the DAC that I am using, was the original DAC that I bought, to convert the digital signal to analog, for my speaker system setup. I then began using it later for my first good headphones setup, the JVC SZ 1000-E's. And before, I was using cheap 100 dollar or less portable amps from Fiio, which were good amps and all, but not really up to snuff for amping 50mm drivers or better.
In essence, the priority was to get a higher quality and more powerful amp. And since I am getting my audio from a digital signal from my computer, the sound quality is actually better then my computer's 3.5mm analog headphone jack. Which means, I am getting higher quality sound then those who would use the 3.5mm jack. So there was no priority to upgrade the DAC yet.
Having said that however, my next priority will be upgrading the DAC, that is plans in the works. I plan to purchase the S.M.S.L M200 DAC, as it will be a welcome complement, to my S.M.S.L SP200 amp.