I haven't heard the D5K, but I am well familiar with the 2K. In fact, TBH I haven't heard all that many cans.
I really liked the 2K, and found the bass (especially sub bass) to be awesome (I'd never heard bass that low before I got the 2K). But their ability to impress me was largely dependent upon the track. I found that I was chasing the sub bass dragon and was not really appreciating a lot of music that didn't slowly and gently massage my ears (e.g. Solar Sailor - Daft Punk).
In comparison, the LCDs don't seem so much to go lower than the 2k, but do so more effortlessly (i.e. faster and harder with more precision). But to my ears, the mid bass of the LCD is what really sets them apart from the 2K. This is where the texture of the bass comes from. Where the tone of the instruments lie. The LCD-2 bass just sounds so much more thick and real. The 2K gives a (false) sense of bass slam, which feels like a small puff of wind in the ear, The LCD doesn't seem to do that (I guess being open), but you actually hear, those low frequencies (all, or at least more of them), rather than (sort of) feel them (as a puff of wind). This make so much more music so much more satisfying (IMO).
FWIW I listen at approximately 80db (peak) most of the time with the LCD, a little higher sometimes. The LCD seems way more satisfying at this volume than the 2K, which I found that I tended to crank a bit more, a bit more often.
I recommend an audition. I could just keep going and going, on and on. But I feel like I'm coming across like a shill or naive fanboy. The reality is I haven't got a great deal of experience with high end gear. In fact, the gear I have now is the best I have ever heard (by far). So I concede that my impressions are totally biased and quiet possibly misleading. hence why I strongly recommend an audition. Whilst I definitely appreciate the difference, I wouldn't expect others (non-enthusiasts) to see the value in the price to performance ratio.
Not that I'm arguing but just wondering - have you heard a Lawton modded Denon?