I too volunteered for the Cable+ review. Unlike others, I opted for the A2A (Aux to Aux) version of the cable for use in my vehicles. I spend two to four hours in my car most days. This means I actually spend more time listening to my car stereo than I do to my home system.
The vehicles are 1) a 2002 Kia Sportage with standard factory speakers and an aftermarket Clarion CZ401 head unit and 2) a 2006 Toyota Tundra with the premium JBL sound system. The head unit has recently be upgraded to a Kenwood DDX9903S. Prior to receiving the Cable+ I have been using an AudioQuest Forrest Aux cable.
My source is a Sony Walkman NWZ-A17. While this is a Hi-Res music player, at $300 it is towards the bottom end of the line. The top end is over $3,000. I point this out because my observations in reference to the A17 may not hold true for other, higher end, models.
Here is the Cable+ in the Tundra
The Cable + performed as advertised. The increase in volume was immediately noticeable. My guess would be about a 6dB increase. Additionally, providing the stereo head unit with the increased current resulted in a smoother more satisfying sound quality then when compared to the Forrest aux cable and simply turning the head unit’s volume up. I can't say much about bass since neither vehicle has anything in the way of subs at this time. What bass I do have sounded fuller and smoother. This also held, but was more pronounced, with the midrange. I don't know if impedance played any part, but stepping up the line voltage did. The top end didn't seem quite as harsh but I didn't try to make any real critical comparisons in a car. I focused more on the overall sound which was more pleasing with the Cable+ powered up.
One issue I found occurred when both the Cable+ and the music player were plugged into a power port. Both the Cable+ and Walkman use 5V USB power. When both are plugged in, even to different 12V ports, there is audible noise coming from the speakers. This occurred in both vehicles but was louder in the Kia since it only has one 12V socket which meant both the Walkman and Cable+ shared a dual USB adapter. Unplugging the Walkman (so it uses its internal battery) eliminated the noise. The potential issue here is running down the music player’s battery.
While $149 may seem like a lot for a cable, if you think of it as a small preamp/gain stage that happens to have integrated cables the price is reasonable. In my vehicles, the improvement is worth the price.