There is thread around here somewhere which explains what, who or when "djent" is... I have to find and read it, I guess ;-)
The stuff you told about the Invader sounds good, because although I really liked the ultra-gain/compressed sound of the Fireball, it is a ony-trick-pony. Interesting that the 150W Invader is cheaper than the 100W Invader here in Germany...
The Invader can do the super-gain/compressed, I usually have tha gain at 9 or 10 o'clock on channel 3 when the high gain mode is engaged.
Channel 3 is my main rhythm channel, but when you have the high gain mode on, channel 2 and 4 have a loooot of gain as well, so you actually have 3 hi-gain channels.
Channel 4 is quite compressed and maybe a bit saggy, it's designed to be more of a lead channel, so it is voiced to suit that. Sounds amazing for singing leads, and the separate EQ's will help to get the best out of every channel.
Channel 2 is an amazing channel as well. Without the hi-gain mode it has a Marshall'ish rock tone, but when you turn the high gain mode on, it also turns into a tight high gain channel. Amazing!
Channel 3, oh yes! An awesome rhythm channel. Has that somewhat scooped tone, but I have had no problems cutting through the mix when needed. Like I mentioned, I usually like to dial in a more Carcass Heartwork oriented tone with this channel, just dial in a healthy dose of presence and you'll be set.
You can get a lot of cool tones with this channel, by just playing with the hi-gain mode (since it also changes the voicing of the channel a bit) and the EQ controls. I just managed to dial the Invader to sound very close to the guitar tone on Bloodbath's newest album... wicked! The hi gain mode is not a must with this channel, and for some types of tones, it is better to leave it off, because like I mentioned, the hi gain mode changes the response and voicing a bit as well, so there's a lot of cool tones to be discovered.
The EQ controls are not anything like the ones on a Recto, so you don't need to worry about that. It's like a "normal" amp when it comes to the controls.(Even though I actually like the Recto EQ section)
The word "djent" is usually used to describe the Meshuggah/Sikth/Bulb type of metal, since nobody really knows what to call that stuff
Oh, and if they haven't changed the Invader 150, I wouldn't get one, since the bright mode only works on channels one and two on it, whereas it works on all of the channels on the Invader 100. For me, the bright mode is always on when going for a good metal rhythm.