What I want:
-Open Back design
-Reference or "fun" sound sig
-Good looking
-Detachable cable (or easy modding for one)
-Around $200

What I am considering:
-Sennheiser HD600 (Can find used for around $200)
-AKG K7XX (Used or wait for another drop)
-Beyerdynamic DT990 Premium (or Pro) 250 (Drop ending tonight or used)
-Phillips Fidelio X2 (Just found out about, not sure)

I am also looking for good amp pairings with the above since all I have is a sub $50 custom tube amp, which is hooked up to a Centrance DacPort LX (which I wont need to upgrade)

And about an amp: Ive heard the Hd600's work well with Bottlehead Crack, which is my main large upgrade on the list

Fun sound signature?  Then rule out the HD 600, K7xx, and Fidelio X2.  That leaves the DT 990 which certainly fits the common description of "fun" (lively sound due to boosted bass and treble, but recessed mid range and potentially fatiguing treble as a result).

Probably should have rephrased that. I want more lively sound without it being too V shaped, also I dont want it to be very fatiguing

Well, "lively" and "fun" refer to V-shaped.  The HD 600 and Fidelio X2 are the opposite, and the K7xx isn't V-shaped either.  But the K7xx doesn't have somewhat laid back treble like the HD 600 and Fidelio X2 do, so it may be your best bet.  That or a DT 880 I'm thinking.