The DSL is the weapon of choice for Gary Holt, Nile and plenty of other super heavy bands I can think of. There's nothing wrong with wanting a new amp but I'd wait until you can save up to get an absolute monster, cutting edge beast of an amp like anything Edgecrusher recommends. He's played through some truly state-of-the-art amps build from the ground up for modern metal. I wouldn't bother with getting anything middle of the road. What you have will do you fine for what you need inexpensively. In the meantime, getting to grips with the tone controls on the DSL, a boost of some kind in front for that super tight chug metalcore is known for. (gain to zero, level and tone up). Tubescreamers are a popular choice but if you're like me, you may not want as much mid hump and prefer to preserve your amp's natural character and just tighten it. For that, an MXR Timmy is pretty flat and then it's just a matter of turning the bass down until it's as tight as you need (then compensate by turning your amp bass up if too much needed to come out) and turning up the treble until the attack is where you need it.
Maybe you'd like more control, something with a selectable mid frequency so you can dial in the mid boost and amount exactly where you want it. I had one custom built and it's a complete one-off unfortunately, but I love the look of the Walrus Audio Emissary which has a selectable mid switch, including where the Tubescreamer would boost. Then there's a few kicking around with a knob that lets you sweep around until you find the sweet spot. Next order of business, there's plenty of EQs both graphic and parametric to choose from to put in your FX loop and fine tune the overall distortion character until it's as brutal and fits the band as much as possible. With graphic, which frequency bands it contains is just as important as the amount of bands. Mesa put out a graphic EQ that uses the same frequencies they have specifically chosen for their amps with built in EQs so you can get the ever popular 750 band cut! I myself have an MXR 10 band and I haven't bought another EQ since as it's so versatile and can do just about anything.
Lastly. Speaker changes make for the most noticeably drastic change in tone. What speakers you're running in your cabinet and even the cabinet itself makes a tremendous world of difference. Almost any deficiency in an otherwise decent hi-gain tone can be solved by changing the cabinet or at least the speakers if not both. Some people find GT-75s too thin or Vintage 30s too nasal and grating so I recommend listening to as many speaker demos online as you can to make the determination if you need a speaker change. My absolute favourite is the GK-85 (The GK100 is quite similar if you can't find one). Smooth, tight, full, clean and powerful. Close seconds are the Eminence Legend (I find it's all the good of a Vintage 30 without any of the bad) or the WGS Veteran 30. Then of course in any cab with more than one speakers you can blend and get the best of both (or four technically!) worlds. The Celestion GK and the Veteran together in my main rig is whole package. Touchdown.
I hope that helps. I'm open to further comments or questions.
