hahah exactly. they are something in-between. LP2 is the true basshead. the over-ear M100 is like if the technical on-ear audiophile M80 had babies w/ the basshead LP2. its classified as modern audiophile: a fun u-shaped sound signature that is very great w/ electronic/house, hip hop, and other stuff that has a good bassline, but can do other things well because the bass is not overpowering or muddy. its a tight accurate bass that doesn't bleed anywhere, so the mids/trebles are still well-defined. i legit just read someone describe it as a better M50, but i would take everyone's opinions w/ a grain of salt & demo yourself. the reason i think the M100 is a good place to start is b/c it is pretty highly rated w/ a solid bass punch. if that's too much bass for you, then you can rule out a lot of things.
sorry i used the basshead term a bit too loosely, but if you want more bass than the M50s, I believe the M50s are already a lil bit U-shaped with slight bass emphasis & recessed mids from what I've read & the ultrasone 580 is kinda bassheady too imo. so i feel like if you want more bass after those two headphones, you would want a top of the class basshead that does bass very well without being overwhelming, which I think M100s.
lol i actually used to almost look down my nose at "basshead" classification, but after listening to the m100, i really loved how a tight bass can really make you wanna jump around. i personally found it really cool how you could hear the details in the lower frequencies that I've not heard before. dunno how to describe audiophilically, but I would highly recommend you to try it as there is a really generous return policy of 60 days.
At $300-350, Sennheiser Momentum & Sony MDR-1r are both solid more mid-centric options with solid bass for closed cans compared to the AKG K550 which is weak in the bass but really shines in treble. some other options are beyerdynamic DT 990, Mr Speakers Mad Dogs, Ultrasone HFI 900... but the list really goes on & on especially since you don't need portability & i don't think you said you only wanted closed. if you go open, there is the the AKG Q701 or Sennheiser HD598 which are highly recommended.
Going to give those some research, kinda liking what I hear about the M100s only problem is I don't have a spot in town that I know of where I can go and demo these. I have decided to send the M50s back, the HFi 580s will most likely be going too. if I could pull the trigger before 10am tomorrow I could have the m100s same day from amazon.