Thanks Randy and others,
The reason I'm trying the Syzygy SLF870 Subwoofer is because it has onboard room equalization. When you set them up initially you just download a free app that Syzygy provides to equalize the subwoofer's frequency response based upon sound samples taken from your actual listening room.
It's then up to you to adjust the output level and crossover frequency, but that should be easy with the Octave RTA app Vade Forrester suggests.
I'm looking to add the missing lower octaves that the Magnepans simply can't reproduce. My experience with the DWM Bass Panel has been that it reinforces the 40-80 Hz. range, but simply can't go any lower. What it does, it does well, but it shares the same limitations as the Magnepans themselves, i.e. nothing much below 40 Hz.
Magnepan says that the DWM is not to be thought of as a subwoofer, but as an improvement to the lower range of their full range panels. Their specs show a lower frequency response essentially the same as their full range panels.
I've had one form or another of Magnepans for over thirty years, and over that same time I've accumulated hundreds of CDs. Unfortunately I wouldn't know what deep bass may be encoded on them that the Magnepans couldn't reveal.
As it turns out, I already have many of the recordings suggested by others here. So I am looking forward to hearing them anew. The Saint-Saens Symphony No. 3 is one I didn't have though, so I ordered the Reference Recordings CD from Amazon earlier today.
-gb-