Okay, vinyl tweaking continues today. A couple of late nights later I've come to some conclusions:
1. The combination of the MO (.9mv) Glider and the high gain (60db) setting of the Lehman Black Cube does overload my MAP-1 preamp.
2. I installed and tested the 50db setting of my VAC-in-the-Box and detected no distortion. This is good news since I was trying to figure out if I had some tracking issues with the Glider setup. This eliminates the mechanical part of the equation.
3. While the VAC-in-the-Box is a reasonable phono preamp, it is not the equal of the Lehman Black Cube. After much auditioning of some reference discs I determined that I would rather use the Black Cube with the 40db setting and just crank up the volume on my MAP-1. In reality, the Black Cube is so quiet that the perceived noise level with the 40db setting and higher preamp volume level is only a smidgen higher. This is an acceptable compromise given the other strengths of the Black Cube.
4. I was being too reticent with the volume control and the 40db setting. I now have an idea of what is the optimum spl and volume setting it needs with this combination.
So, I've come full circle and have learned quite a bit about my vinyl rig I didn't know before. I think I can live with the current setup but I am thinking about a possible purchase of the Monolithic PS-1 phono preamp. This purchase would improve the perceived signal to noise ratio because of the 53db setting of the preamp. This should be a near perfect match to my Glider MO. All the reviews seem to point to this being a better phono preamp than the Black Cube.