My advice on how I have gained 6 stone in weight in 4 years. It may help you.

This routine is  mainly HIT with a little more volume than most die hard HIT trainers would use. It has worked for me so try it you may get surprised give it 12 weeks to see if you like it or not. It is nothing fancy just basic common sense advice.
 
Try a 3 days a week routine. keep your sessions to roughly 45 mins no more  than 60 mins at a time.m Try the following split. Chest & Triceps. Back & Biceps. Legs & Shoulders. Or mix it round to what ever suits you.
Train Monday, Wed and Fri
Do 2 or 3 exercises per large body parts per session.
And 1 to 2 exercises per small body parts per session.

An example is

Chest.
Bench Press    4 x 6 - 10
Incline Dumbell Press  3 x 6 - 10
Dips  3 x 6 - 10

Triceps
Close grip Bench presses   3 x 6 - 10
Cable pushdowns               3 x 6 - 10

Your rep range should be 6 - 10 reps
Do 1 or 2 warm up sets of 12 - 15 reps dont include these as work sets
Do no less than 3 and no more than 4 work sets per exercise.
After your warm up sets go straight into your heavest weight for 6 reps to failure. The next set you may have to lower the weight to get between 6 - 10 reps again to failure.
All work sets should be trained to failure within the rep range of 6 - 10 reps.
Always use compound exercises first in your routine.
Rest roughly 2 to 3 mins between compound exercises.
Rest roughly 1 min between isolation exercises.
Once a week try the odd drop set or forced set but only for one set.
Eat plenty of protein use powder if needs be.
Sleep 6 - 8 hours a night
Finally If your ready for it mature enough, know the risks and are over 21 years old then you can use 500 mg of Test a week.

Do all this and you will grow.  This is what I have roughly done for 4 years now and I have put on six stone in weight. If it worked for me it will work for you.

My body is like a Walking Chemical Factory.

its nothin like HIT really tho is it mate..
looks decent enough tho.
and if its worked for u then nice one :-)

My Youtube Vids

The MRM Way

but the difference in gaining 6 stone isnt to do with routine really its diet.

and have you got any pics showing the difference? would be good

not really at all HIT - HIT is based around 1 set on each muscle group.

Will work, of course it will, but only if paired with a good diet, test will obviously help too (as long as taken correctly)

My journal, with pics.

http://www.muscletalk.co.uk/tm.aspx?m=3546471