I own both Cresyn & porta pro 2 (different name, but the same sound ). You can't really compare those cans. Cresyns are good if you need more isolation & punchy bass. I found them to be perfect phones for electronic, industrial etc. Koss have no real isolation due to open design & are better for rock. Both have great bass - pretty good with amp & controlled, good amount of details. Cresyn have better mids for sure. Hp600 & Porta have some troubles with highs - they are shrill sometimes.
I bought my cresyns for 10$ at discount - so they are ideal for everyday use (have 'em 6 month). Koss costed me 20, but i use them 3 years - changed pads & cable, but they work fine. Probably they are more durable then Cresyns (time will show).
Though i prefer Cresyns in the terms of design & sound signature. They are also louder. If you have some questions - write the PM.