John Hillig does an excellent job on Haflers. He's been creating successful Hafler amp and preamp mods for 30plus years, knows what he's doing. I have used his design and even cut Haflers in half (Quarterlers?) to create two mono amps each with massive power supplies.
But even the very best mods cannot overcome the biggest problem with Haflers. They lack very fine detail of modern amps and any dynamic slam at all. I don't know what can be done to improve this. It's just not there.
With the great selection of modern amps at great prices, the Haflers just don't make sense in a full range system. That said, they might work OK with subwoofers operating below 35hz with steep crossovers. Not much dynamic requirements down there, just pumping out bass from a big subwoofer.
But even the very best mods cannot overcome the biggest problem with Haflers. They lack very fine detail of modern amps and any dynamic slam at all. I don't know what can be done to improve this. It's just not there.
With the great selection of modern amps at great prices, the Haflers just don't make sense in a full range system. That said, they might work OK with subwoofers operating below 35hz with steep crossovers. Not much dynamic requirements down there, just pumping out bass from a big subwoofer.