Ok guys, just to clear it up. DSP stands for Digital Signal Processing.
The signal coming from the HU is very distorted and adjusted to hide the deficiencies of the standard speakers. You may have noticed if you have let's say the RNS 510, the base tends to drop off compared to the rest of the sound coming from your speakers as you turn the volume up.
Being active, what these units do is smooth the signal from the HU providing as clean a signal as possible to the amplifiers via RCA's. If you will, they iron out all the imperfections. They also provide a built in crossover allowing you to fine tune your system.
Normal LOC's in retrospect are passive and just convert the existing signal to an RCA signal without any signal correction.
Here is a bit of blurb from Audison regarding the Bit Ten
"Audison Bit Ten
bit Ten is a multi-function digital processor featuring analog input, capable of transforming ordinary OEM or after-market system into a high-performance system. Provided with a 32 bit, 147 MHz clock speed DSP as well as 24 bit A/D and D/A converters, bit Ten is controlled by a software especially developed for signal treatment according to the vehicle acoustic peculiarities. Setting the parameters of each input single channel, setting the delays according to the listening position, adjusting crossovers and equalizers for each of the 5 output channels; all of these operations can be managed by the PC.
During the installation phase, after converting the analog signal into digital, bit Ten automatically reconstructs a digital full-bandwidth stereo signal; de-equalizes the frequency response and, if necessary, reconstructs the central and subwoofer channels. The user can configure the output mode of each channel relative to the installed system.
It is designed to be connected with the DRC, Digital Remote Control (optional)."
As I wanted the purest and cleanest signal I could get from my RNS510, I have opted to go with the Bit Ten D.
Hope this helps?