@213running - Yes, it is true of every 2 channel amp. When run in bridged mode, it is not specifically designed to be stable to when run at lower impedances. The following is specifically stated on Schiit's website if you click on the FAQ section of the Vidar:
http://www.schiit.com/products/vidar
So what happens if I have 2 ohm speakers? You didn’t rate Vidar for 2 ohms.
No, we didn’t. Because speakers that are rated below 4 ohms are pretty rare. The bottom line is that Vidar will run 2 ohm speakers, but it may run into its protection and turn itself off.
Same for 4 ohms when running monoblocks?
Yes. Again, Vidar will probably work fine at sane volumes, but at higher output, you may trigger the protection.
I never recommended that the Parasound A21 should be run in bridged mode. I did state that the XPA-1 monoblock (and probably every other "true" monoblock) will be stable at lower impedances because the circuit and power supply rails are specifically designed to be stable at these impedances.
You seem to be contradicting yourself in stating that stereo amps should not be bridge, but then go on to state that the Vidar stereo amp is fine bridged. If you say they have tested the Vidar in bridged mode, then fine. This is not usually the case.
I only recommended the A21 because the OP is looking for either a monoblock or good stereo amp.