I think it depends on the amp. Some sound shitty at low volumes and some don't. It also depends if by "ultimate" you mean regardless of price, what you mean by low volumes and the tolerance of those around you. Alot of high gain amps sound pretty good at low volumes nowadays, it's unlikely that the bottleneck in your chain will be there imo. But if you're a perfectionist the isocab might be a good idea.