It is balanced or not?

Running the sound through the JBL MSC1 is definitely going to degrade the sound quality of the Emotiva DAC, but if that's all you have, that's what you are gonna have to use. 

Is the amp better to use as stereo?  Generally speaking, yes.  It really depends on the speakers and if they drop below 8 ohms, but usually stereo amps do not perform as well in bridged mode.

Generally, a dedicated balanced/differential amp will have power from both the +(RED) and -(BLACK) speaker posts.  In this situation, you cannot bridge amp channels because they are already, in a sense, bridged. 

The service manual does not give a complete schematic, but if you look at page 6-3, you can see the Output Stage schematic.  On the right side of the schematic you can see the output connected to one speaker binding post.  The other speaker binding post is shunted directly to ground, so this is a single ended amp (even though the input stage is balanced).

Too many sources and amps are really SE main circuitry with opamps on the input or output to make them pseudo balanced (xlr) just to suck in the xlr freaks.

In these cases stick with SE, and you bypass these opamps (best opamp is no opamp). You only need balanced (xlr) if your running 10mts of interconnect through bad surroundings with lots of rf emitting equipment.
Cheers George

@auxinput: Well, I think the best way that the Crown D-75 can sound is in stereo, because each amplifier has its connection balanced or unbalanced and is not divided for 2 amps, as it is on page 6-1 of the service manual; in My opinion, the best way they can sound is to put them both in stereo and connect the right speaker on channel 2 of one of them and the left speaker on channel 1 on the other, both in stereo, so each internal amp has its conection. what did you think? thanks :-) 

yeah, that sounds like a good plan.  If you have two D-75 amps, use one for left speaker and use the other amp for right speaker.  That way, you are not sharing a single amp power supply for both speakers.

@auxinput: yes, but not in mono, in dual channel but using one of the amps for a speaker :-)