I'm not familiar with your speakers. For a bit more money, you might find a McCormack ss amp or a VTL tube amp that will work well with a passive pre.
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Thanks for your posts
I was not able to get output voltage for the DAC. Based on what I knew, Tim Stinson at Luminous sent me an Axiom with a value of 2.5K (the resistor?). That has worked out great--I got a big improvement in clarity using the Axiom instead of the NAD's preamp. Tim (who was great to work with) said the Axiom I have should probably also work fine with a c272, although it is not the same as c320BEE.
Notice too that sensititity is proportional to wattage ratings. Often, within a manufacturer's lineup, the sensisitivity rating goes down (up numerically) as the amps get bigger. Often, there's a difference in ratings between balanced (XLR) and single-ended (RCA) connections, when that's an option.
Gotta admit that those Meridian 605's are mighty sensitive for 150 watts.
Generally for a passive, the output of the source is critical with at least 1.5V and an output impedance less than 200 ohms being favourable. If there is an impedance mismatch, frequency extremes get rolled off.
Most resistive passives are about 10K input impedance but 100K are available, including some Noble pots which is the brand reported to be used in the Axiom. Higher impedance is an easier load but there are trade-offs.
Then, speaker efficiency plays a part too. So does the length and capacitance of the cables....
What was your question?
First question, why the passive volume control when you have a good integrated?
Second question, why not consider better speakers instead of electronics? You'll still keep your sub, of course. Depending on your room size and listening levels, I'd consider changing speakers first.
If you're sold on new electronics and like NAD, why not step up the power with another integrated.
The passive volume control ($140) was an experiment. I was thinking about integrated amps with passive line stages (like Creek 5350) and wanted to see what would happen with sub inserted between passive pre and power amp--would long sub cable be OK. The sound improvement with the Axiom was, to my ears, dramatic and very enjoyable. It sounded so good that I thought, with a little more power I can stop (ha!). I don't need multiple inputs and don't care about remote
Since it's a passive device, it'd be easy to measure its input and output resistance with a digital ohmmeter. My concern with passives (I use one in my office system) is impedance matching.
I'm a believer in more watts being better, but the congestion you describe sounds like a speaker/room issue to me. That being said, by all means try more watts. I'm a fan of Bryston and ATI amps; ATI being the better value.