I asked David about it along with my other questions but here his response:
"DA-151 and 152 are not replacing each other, 151 is not shoing up on
our web site because we almost ran out of it, as we currently only
have one unit available at the moment.
As for the difference, DA-152 is indeed pretty much a meld of HA-171
and DA-151, but HA-171 does offer much more flexible connection
options as it allows you to connect to any DACs or other sources while
DA-152 only allow USB for input."
So yea there you go. David is a great guy and answers your question pretty fast.
I am mainly curious as whether the DA-152 can drive high impedence headphones like the HD800 or T1 effectivly. I really don't want to upgrade the back end that much =\