I've been reading this thread with interest as I have been trying to decide between these two recorders myself. I use the 722 for work on a regular basis and just love it but was excited about DSD and figured it would be nice to save a little money on the Korg. So, I ordered the MR1k before traveling to do some important personal recordings.
Here are my impressions:
Construction is nice: case and controls are certainly not as solid as the Sound Devices but not your typical cheap plastic "pro" recorder. Included carrying bag is very handy and functional. But, when I plugged in some mics (ME67 & neumann kms105), I was pretty disappointed. To my ears the internal pres have too much hiss, sound pretty thin and, as mentioned by others, were really hot and prone to spiking. I panicked a bit and wound up borrowing a Sound Devices 302 to use as a front-end for my recordings. Results were great with this set-up but, not having an external preamp of my own, I've pretty much decided to return the Korg. I really need a 1 box solution and just don't see the point of making higher resolution recordings with compromised sound quality coming in. I tend to record pretty quiet sources (not rock concerts) so noisey preamps are quite distracting and make editing a nightmare. I may wait on buying a Sound Devices (probably opt for a 702) as I'd still be really curious to hear the MR1k with preamp mods.
I really wanted this recorder to measure up to (or surpass!) the 722 but I just don't feel like it’s in the same league sound wise. If I'm going to spend this much money on a recorder, I feel that I should be able to make a good clean recording with it out of the box. Sound Devices, as a company, seems to share this philosophy. With Korg, I get the sense that they're hedging their bets a little: knowing that many users will just want the MR1k for mastering or will have their own high-end external preamps and decided to cut costs in this area.
Hope this is helpful for others juggling these options.
-Nick