How do I hook up 2 preamps to one amp

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When you use the splitter you are effectively hooking the 2 preamp outputs together which is never a good idea.

I haven't used a tape loop in a while but I don't believe that would work as described. The tape in from the Lexicon would be controlled by the NAD volume control if you use the regular outputs. It is the tape out that isn't affected by the volume control but if you use that then you won't be able to control the volume for music either.

Use the normal pre outputs from the NAD to the input of the amp. Take the Lexicon front L and R output and put into any unused input on the NAD including tape in. Choose that input when watching videos. When you do, set the volume control on the NAD so it matches the level when you have the Lexicon hooked directly to the amp.

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Kartez and Herman, tell me if I'm wrong but...aren't most Lexicon units superior to most NAD's? Why not lose the NAD?

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I considered that too but since I have no experience with either decided not to comment.

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Herman has it right. Line out to line in always works and tape outs are independent of front panel controls. But based on the rather funky arrangement and weird signal flow, combined with probable tape output selectors, lots of ways to get confused and have no sound (flipping buttons madly trying to get audio until YES full output into the amp). Simple is always better sound anyway, use everything through the Lexicon....It must have a 2 channel mode......

Brad