Performance
Performance from the CDX-M600s preamp outputs is comparable to the majority of the units that we regularly see with 2.5V of undistorted output — nearly 94 dB of usable dynamic range and a source impedance of about 250 ohms. The subwoofer outputs are capable of about 2.2V of undistorted output and are essentially full-range outputs. Response above about 10 kHz on the sub outs rolls off rather quickly, but as long as you’re driving a subwoofer, it won’t be an issue.

Of course, the 50Wx4 rating on the internal amps is a bit optimistic, but that’s nothing new in the head unit market. We saw a maximum of 38Wx4 with all channels driven into 4 ohms. While this is only equates to a difference of about 1 dB from the 50W rating, distortion at this power level approaches 40 percent. Viewed with sensible distortion limits, the M600’s internal amps are capable of about 18Wx4 at 1% THD+N or about 25Wx4 at 10% THD+N. Again, this is right in line with most of the other competing head units, and should prove adequate for anything short of a subwoofer or large midbass driver.

While they still fall well short of their ratings, head units’ internal amps are becoming more powerful. More power means more heat, and the typical dashboard/console location isn’t famous for its ventilation properties. Sony is one of the few manufacturers thus far that has gone to the effort of providing a well-designed heat sink for the internal amps. It appears to be a cast-aluminum piece with a large number of fins; just what’s needed to effectively dissipate heat.

User Evaluation
There are several things about this unit that I really like. First and foremost is the wireless remote. While the M600’s control surface feels a bit dodgy, the remote almost seems to know what you want before you press the button.

The next cool feature is found on the other side of the faceplate. The whole blackout concept is pretty much self-explanatory. When the unit is switched off, the faceplate is a bit shinier than the average radio-delete plate, but it should be sufficient to give thieves the impression that there’s nothing to steal. Moving the control surface to the other side opens up a world of display space so the faceplate really comes to life when power is switched on. There are several display modes, which are all a little flashy for my tastes, but Sony didn’t fail to make the important stuff very large and legible.

My final bonus point is awarded to the faceplate’s operating mechanism. This mechanism is simple to the point of elegance. The faceplate is hinged near the bottom and flips outward, leaving the control surface at an angle that resembles that of a computer keyboard. This leaves the CD loading slot exposed and allows the operator to look at the control surface pretty much head-on. Most of the other units provide the option of positioning the faceplate in this manner or at various other angles. A lot of options are great until you find the one that makes the most sense, and then the rest are just superfluous junk that congests your user interface. I think that this is one case where Sony did away with the congestion and just made the most sensible optional the standard position.