Is my amp "High Current"?

yes it is

Yes, McCormack amps are high current design.

Steve at SMc Audio (where mods were done) will gladly talk to you. You have a very NICE amp there!! Have fun!!! Only thing I like better is tube amp, but for solid state McCormack is great!!

What is the definition of "high current" amp?

High Current is most commonly used to describe an amp with the ability to deliver increasing amounts of current into low impedence loads. The ideal amp would deliver twice the current as the load halves. For example, 100 watts into 8 ohms and 200 watts into 4. Many designs are able to deliver brief peak amounts of current far in excess of their rating, but can't sustain current demands for very long.

You can check the specs on the amplifier for "amps" no joke. That tells you if the peak current is high lets say 40 amps but big SS are higher. Whereas the cheap 5 lb 100wpc uses a power transformer delivering 100 volts which is all the amperage it's going to get vs, a 1kilo volt transformer -now the amp weighs closer to 100 lbs more - and has 1,000 volts to draw on. That's why there is a warning not to try to service it yourself "Lethal Voltage". The advantage is that you have head room for demanding passages.