That's software isn't it ?
Regardless, software firmware, the processors is more than likely the biggest difference.
Now if the Processors are the sam then I don't know what they have done to bog the 34 down.
The system board and processor in the HR34 is different than the HR44. The HR44, in addition to a faster processor has consolidated the hardware into a much more efficient system board. This is likely the reason the HR44 is leaps and bounds more stable and faster than the HR34.
Why DirecTV is still installing hardware (HR34) they know is not functioning properly, due to its original design limitations, is beyond me.