I own a Tempest II Magnum. Since the III was released I communicated with Rogue to find out what the differences are and what the update cost is. From what I was told, there is the headphone amps you mention plus a switchable active line stage. The II's line stage is purely passive. If your source components have enough output to drive the amp you'll be fine with the II. With the III you can get an additonal 10 dB of gain. It's not tubed gain but rather Rogue uses an op amp chip made by Analog Devices.
Bottom line is that if you don't use the active line stage the II and III are the same. With the active stage I would imagine there must be a difference because you are adding a solid state active device.
I ultimately decided not to convert my II into a III. I have a headphone amp, so I don't need that. I always have enough input voltage on phono and tuner, and almost always have enough input voltage on CD. I ultimately decided tht if I wanted some line level gain I woud add a seperate Pre amp. So far I have not taken that route. In the past I owned a Pass Aleph P preamp. I suppose if I found and Aleph P or an Aleph L I might jump on it.
I suppose how efficient your speakers are will make a difference.
Bottom line is that if you don't use the active line stage the II and III are the same. With the active stage I would imagine there must be a difference because you are adding a solid state active device.
I ultimately decided not to convert my II into a III. I have a headphone amp, so I don't need that. I always have enough input voltage on phono and tuner, and almost always have enough input voltage on CD. I ultimately decided tht if I wanted some line level gain I woud add a seperate Pre amp. So far I have not taken that route. In the past I owned a Pass Aleph P preamp. I suppose if I found and Aleph P or an Aleph L I might jump on it.
I suppose how efficient your speakers are will make a difference.