NathL

Either the ATH-M40X or their larger brother the M50Xs. Both are under £90 at this point in time on Amazon, and are accurate and slightly bass-heavy in my opinion (I own a pair), which is perfect for any electronic music, whether it be Trap as you've suggested or other genres. Something else like the Sennheiser HD 380 Pros wouldn't go amiss either. People have commented that the bass is tight as well as the highs, even though they are older than both the Audio-Technica models.

Either the ATH-M40X or their larger brother the M50Xs. Both are under £90 at this point in time on Amazon, and are accurate and slightly bass-heavy in my opinion (I own a pair), which is perfect for any electronic music, whether it be Trap as you've suggested or other genres. Something else like the Sennheiser HD 380 Pros wouldn't go amiss either. People have commented that the bass is tight as well as the highs, even though they are older than both the Audio-Technica models.

First off, 700W is plenty enough; you're currently drawing around 250W, since the 6300 draws 100W, and the 750ti draws around 60W (and the MB drawing 70ish) so you'll be fine with any GPU you get as long as it's not something stupid like a R9 295X2, so you can most likely keep the PSU. Since you've got a black edition 6300, it's most likely that it'll still perform well, but you could upgrade to a 4690K in the future, since that's in a sweet spot for price-performance. Despite that, it's still most likely that It won't bottleneck if you've got a mid-range AMD or nVIDIA card like you do (750ti), and probably won't even if you go up to 970 range - after all, it is a 6 core processor. 
 
So; GPU choices - there's no real point going crossfire or SLI, with this - due to you paying too much for what you're getting in the end. So, you could get a R9 280X - as that'll work well with the 6300, as well as not being too power hungry like the 290X. You could even push it with a 970 or 285, or even potentially a 290.

http://www.gsmarena.com/ - In my opinion the best place that states Mobile specs. You can also compare between phones.

http://www.gsmarena.com/ - In my opinion the best place that states Mobile specs. You can also compare between phones.

Meanwhile, my pc that takes 250-400w. Gonna need that PSU.