I went that route also. I got the HRT and used it- but the upgrade in sound was marginal. The RR2150 has a decent DAC, so I imagine the HRT "upgrade" didn't do much. However I then researched and bought a Grant Fidelity DAC-09 ($225 shipped), which made a big difference. They are also an AK sponsor.
The DAC-09 has a lot of features, including a tube output and can also be used as a preamp. Check it out on their web site. For me it was a great match for the Outlaw...