The Mjolnir isn't a bad choice for the LCD-X, but it does have it's own signature. There's no harshness in the upper registers, but there is a lot of detail. There's some tradeoff of thicker mids for an airy sound. I don't think you're going to find an amp with a larger soundstage, but there's a tradeoff. If the LCD-3 is your signature, the LCD-X moves away from that mid-centric lushness, and the Mjolnir keep pushing in the same direction. I think the Mjolnir pairs with the LCD-2>LCD-3>LCD-X.
I'd like to find a neutral amp with a large soundstage, and very tight control over the LCD-X, that adds a little richness in the mids for less than $1000. That doesn't seem unreasonable given the LCD-X's efficiency.
The Geek Pulse sounds interesting--have any prototypes been reviewed (with direct comparisons)? You can probably expect a very good DAC with a good amp circuit--may be just fine for the LCD-X.
Might wanna take a loot at the SA-31.
Big and expansive soundstage: check
Rich mids: check
Despite its warmish sound signature, it retains a high clarity throughout the whole spectrum so it shouldn't decrease the perception of "air" (which the LCD-X still lacks, IMO).