Best Exercise To Improve Capability Of Handling Heavy Amps

Pending doctor’s approval, not necessarily for strength but gets the distortion out of your lower back so you don’t blow it up

Wall stretch or more advanced Counter stretch

a 90-100 lbs component gets especially heavy vs something that's like 60 lbs. 

Curls are very good for strength, Deadlifts are very good for overall strength. 

Use dumbbells' whenever you can. They are the best. 

Why not something like this?

https://www.vevor.com/hydraulic-scissor-cart-c_10488/vevor-hydraulic-lift-table-cart-330lbs-capacity-50-lifting-height-manual-double-scissor-lift-table-with-4-wheels-and-non-slip-pad-hydraulic-scissor-cart-for-material-handling-and-transportation-p_010135843528?adp=gmc&utm_source=google&utm_medium=cpc&utm_id=18849210433&ad_group=143670173936&ad_id=633787071277&utm_term=&gad_source=1&gclid=EAIaIQobChMIwca9nKLmiwMV95XuAR3oGxS6EAQYAiABEgJ53_D_BwE

As a retired Primary Care Physician I would recommend starting with a Physical Therapist, particularly one with experience in Occupational Medicine.  The major health risk here would be blowing your back out.  Even if you don’t do serious structural damage to your back such rupture a disc, you could do soft tissue muscle damage to the back that will cause painful spasms and limit you.  Strength training alone won’t do it.  Gyms are filled with muscle bound studs with chronic back pain.  Stretching exercises for your back and proper lifting techniques are more important.  I would also suggest using whatever equipment is available or that therapist may recommended to help lifting .  Lifting a 109 pound amp from the floor and carrying it might look impressive to onlookers and boost your ego but I foresee a lifetime of misery with back pain unless you take precautions 

As a longtime gym rat who originally started lifting to combat chronic back pain, I recommend deadlifts, bent rows (both dumbbells and barbell) and a lot of core exercises.  

I will add that whenever you are lifting something heavy, don't attempt to "jerk" the weight up and make sure you are warmed up in general.