That's not entirely true.
Even though I listen with my North Star DAC and GS-1 amp, the O2 transportable sounds and measures as good anything mentioned here and it's really cheap to build or buy.
Another 650s portable worth mentioning is the Portaphile V2 Maxxed, which is my favorite power failure amp. Here's a pic I took by flashlight during one of the NY blackouts.... (the blue cable is acting as the FM antenna, pulling in a station from 42mi away)
the Portaphile V2 Maxxed is half the size of the O2, runs off a single 9V battery and only lacks the very last bit of resolution of the O2.
Before you spend any more money, you might want to pick up a cheap O DAC and O2 amp as a basis of comparison.
Once you hear this level of resolution, it will be hard to settle for less.