I mostly agree with Island, except for the part about the bass being doubled. I've been researching the exact same thing recently.
If you have both inputs connected there are two issues:
1) Crossover freq. With the II, each input has the same crossover point as you dial it in. This could be a problem depending on your main speaker and where you set the xover. For HT, the THX specs call for 80hz as the correct xover for the .1 channel. If you have full range speakers this is likely too high and you will have to manually adjust for each mode. For either the II or III keeping them both connected should not matter that much because in two channel mode your pre/pro should shut down the .1 output so no issue. In HT mode, the low level input will reproduce the .1 channel and the high level inputs will reinforce the left/right mains subject to the xover concerns earlier. The III allows you to bypass completely the xover for the low level input making it ideal for a 2-ch / HT combination.
2) Is level matching. With the II there is only one level control. You can set it for 2-ch with the high-level inputs and you should be able to match the .1 level with the pre/pro .1 output control. The III has separate level controls for each input.
My pick is a Stentor III
btw. Eric at REL tech support is great to communicate with. He responds in less than 24 hrs to your questions.
If you have both inputs connected there are two issues:
1) Crossover freq. With the II, each input has the same crossover point as you dial it in. This could be a problem depending on your main speaker and where you set the xover. For HT, the THX specs call for 80hz as the correct xover for the .1 channel. If you have full range speakers this is likely too high and you will have to manually adjust for each mode. For either the II or III keeping them both connected should not matter that much because in two channel mode your pre/pro should shut down the .1 output so no issue. In HT mode, the low level input will reproduce the .1 channel and the high level inputs will reinforce the left/right mains subject to the xover concerns earlier. The III allows you to bypass completely the xover for the low level input making it ideal for a 2-ch / HT combination.
2) Is level matching. With the II there is only one level control. You can set it for 2-ch with the high-level inputs and you should be able to match the .1 level with the pre/pro .1 output control. The III has separate level controls for each input.
My pick is a Stentor III
btw. Eric at REL tech support is great to communicate with. He responds in less than 24 hrs to your questions.