Damn this achievement hard in the face! But I've got it now! A big tip; if the game refuses to let you hit the triple taps, smash the turntable HARD AGAINST THE FLOOR. The game will then make you look like a noob because you'll do awesome next time. That's how I unlocked it.
But seriously, let's see if I can lend a hand like I did with Beats & Pieces on DJ Hero 1...
Power Deck; Euphoria Deck
Preparation; Make sure your batteries will last the song. Obvious, but you'd be surprised at how many times my batteries have died during an FC on Guitar Hero. Test to make sure all buttons are working correctly. CALIBRATE!
All set? OK, let's do this!
The first part of the song is really easy, but don't let that fool you. At about 320 notes in, the stupid part happens; 2 blues followed by 6(5?) blue taps leading into a little awkward section of B-R, G-something and a "what's it called flick down blue".
This part will get you. You can sit there saying "Screw you Callum, you're just bad at the game, that part is loleasy!". You may be right about me being bad at the game, but that part will hit you in the face and then take the sweets from your kids. If you don't have kids, it'll follow up the punch with a swift kick in the nads. Hard.
So, it's a good idea to go for your 400 streak AFTER that part. Like right after. But, as is the way with this song the next part isn't so easy. It's a series of triple taps, ranging from blues to B-R, G-B, etc. It's not impossible, but it can catch you off guard. It's vital you nail from the middle of this section onwards though, as you'll get your 400 just before a very tiny, but uncomfortable finger spazzing section.
Have you hit that now? If you've looked at this while playing, PAUSE! But no, you wouldn't be that silly, would you?
After this, the next 250 or so notes are easy. Use Euphoria at the cross fading section, depending on how much you have (I'd recommended hitting the first Euphoria phrase and the third at least), use it at the start or midway through. At the end of this phrase is another little awkward triple tap section. Be sure you're ready for this, but don't get nervous... There's a section for that right about... now!
The slow part. I hate this part. You know why? Because my heart starts beating, my bowels start shifting, and my hands get wetter than a duck. I can barely see from the sweat streaming down my face.
Keep cool here, seriously. You'll probably hit 300 here, and then paralysis may try to kick in. Fight it! There's another cross fading section coming up in a second, and this is where you use your own initiative and decide whether you want to use Euphoria on it. It's not hard though and you should do fine, but as you may be nervous, having to work the cross fader can add a little bit more pressure.
At the end of the cross fading section, there's a triple tap section... again... This one has you press all 3 buttons, which is where I always went wrong. Try to get your fingers posistioned for this. Hit this and you'll be at about 380 notes, and the next 20 are really easy.
There you go. Reading through, I doubt this'll help, but I'll keep it here anyway. Congrats, you've wasted your time reading this. If it helped, great! If not, then I'm sorry. I'll refund the minutes to your Paypal, somehow.
Oh, one more thing. If you get to the 2nd cross fading section with only about 300 notes, don't Euphoria through it, as you'll have to use it on the next cross fading section as it has a very awkward spike. Also, that awkward bit I told you about earlier will show up. I forget how it looks, but you'll know it when you miss it.
Right, I'm off to apologise to my now possibly broken turntable. Toodles!
EDIT: "I'll be a little more serious now.
So in summary; Start your 400 streak run from about 325 notes into the song (Where the awkward part happens detailed in the guide.
Learn how to hit all the triples at the start of your run. They're difficult but with a little practice and figuring out the timing window, they aren't a huge threat.
At the big cross fading section, activate Euphoria right before they get fast. Using the Euphoria Deck will guarantee that you will get all the way through this section even with half a bar of Euphoria.
Do not miss the triples after this section. Again, practice this part until you have it down to an art. You really don't want to screw up here because you weren't so sure that you could hit it.
If you have Euphoria again, just use it. It takes the pressure off of you a little bit, which is always helpful.
The most awkward part of the run; the last triple taps section. This is made ten times harder due to the fact you'll be at a 360+ streak. Once again, practice until it's down to an art.
The rest is simple, but try not to lose focus."