I was wondering about this a while ago.
I believe the answer is - the units with "Ultimate" written in red were more limited edition with even higher-quality parts.
For example, the Luxman L-540 has an industrial-grade IE power transformer. Very similar to what companies like Nissyo produce. (for converting 120 or 110 v to 100v). These are often better than torodial power transformers and may last / funtion properly up to 20 years plus.
The older models under alpine/luxman for the most part were not very impressive. Especially the build quality. When they wanted to become a more premium brand, the vintage VU meters, heavy casework, and large custom heatsinks were proably a copied concept from flagship units sold by Sony and Pioneer, who were doing extremely well in terms of number of units sold vs all other Japanese brands at the time.