Change from Spectral

Why do you need to change?

That "using both a pre and amps dc-coupled is NOT at all a good match." is news to me. Spectral, at least in the past, only made DC coupled pre's and amps, as well as Atma-sphere, Krell, etc.. I suspect (for some time, it was srongly recommended) that Specratal would want their customers to buy and use their gear together. Some have argued that balanced, low impedance, direct-coupled designs have some advantages. Many DC couple designs use a servo-mechanism that would might offer greater protection from DC leakage than caps might provide. I'm sure SF knows what's best for their gear, but I sure would like to know the reasons behind SF's recommendation.

TBG, I thought the SP6 was cap coupled? I'm not familiar with the Electro-Research amp. If the amp was DC coupled I'm not surprised you had a problem when DC leaked from the ARC cap coupled pre. This example only supports my idea that DC coupled amps are best used with DC coupled pre's.