you need to vary rep ranges and incorporate some workouts of higher reps. you won't lose muscle mass or strength by taking some time off to do light work. as long as you stimulate the muscles, you will encourage growth/ development. targeting the 15 + rep range is very good support for stabilizer muscles and tendons. if you constantly overload your joints/ tendons week after week, day after day with high volume weights, your tendons will not be able to handle the excess stress and you will run into problems.
When it comes to lifting, you have to think intelligently with your head, not your ego. Not to say that you have an ego of course, but case in point... getting 6-8 reps each week with heavy weights is impressive, but stressful on the joints if done repeatedly. Also, sticking to the same rep range week after week will eventually decrease the effectiveness of your workout, as your body will adapt.
Try something like this. A 4 week high, 2 week low volume type split. For one month, focus on your HIT workouts, targeting various rep ranges each week (i.e. 10, 6, 8, 4), then the next coupla weeks follow up with 12-15 rep ranges to let your body recuperate. You can still even stick with HIT, just lighten the loads a bit. Doing pre-exhaust, supersets, etc w lower weights will not be easy and you will still get a great workout from it.
You might also want to look into following HST related principles. Good luck to ya....