Could not download that...
Isn't there a youtube video for the tune(snippet) you wanted us to hear?
A subbass is just some low-end humming sound in the 40Hz-60Hz range, there isn't a big mystery to it. You probably want to know how to make a low-mid bass and then add a sub underneath???
__ Check my soundcloud (exclusive tracks on there)
So you want to create techstep bass madness...
It's not really something you can learn from a tutorial as it takes quite a lot of trial and error. This is an "advanced" topic!
Use lots of different bass sounds and make some crazy patterns: pitching, sliding, wobbling, .... To keep things controllable and cpu-friendly I'd use samples to do this. Don't use samples from other tunes that already sound they way you want them to sound. Take simple basses which have a good low end and are long enough to let you mess with them (pitching, gliding, ....). You might need as many as 20-30 sounds to get enough variation in your bassline.
For starters I'd take just a couple.
Don't worry if it doesn't sound like the example yet, the hard work is about to begin:
Route all different bass sounds into a mixer channel let's say channel 1, this channel then gets routed into 3 other channels let's say 2,3 and 4 (one for sub, one for mid, one for hi mids) and you should not route channel 1 to the master.
In channel 2 you want to make the sub, so you low-pass everything under let's say 100HZ and compress it. No other shit on there, no distortion, reverb or whatever. Make this channel mono.
In channel 3 you want to process the low-mids, this is the stuff that gives the taste.
band-pass 90Hz-400Hz to get the part of the spectrum you need (values can be different, see what works for you).
You can use distortion, compression, saturation,... try whatever you like. I don't have the magic formula. This channel can stay in normal stereo, if you make it mono the result sounds dull.
In channel 4 you process the hi-mids: hi-pass at 400Hz, extra stereo is allowed on this part, light reverb is ok too. This part needs to give the bass some bite so you want it to have some good distortion. Roll off the hi end at around 1000Hz because you want to keep room for other stuff.
Finally you should route channel 2,3 and 4 into channel 5 (and not to the master). In channel 5 you set up some multiband compression (and if needed saturation, warmifier, ...) to glue the 3 bass parts together again. Channel 5 goes to the master again.
The midbass part should get some sidechaining because it will mess up your kick (and eventually snare)drum so you want to make room for the kick/snare whenever it/they hit(s). Sidechaining is a whole different story, but if you use the most recent version of FL you can check youtube for a very good video tutorial on that topic.
There you go.
__ Check my soundcloud (exclusive tracks on there)