Need Help choosing Stepped attenuators

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I need some stepped attenuators for use as gain (not volume) controls on some DIY power amps.

I'm looking at these on ebay: New 21 Step Attenuator Potentiometer 10K Log Stereo - eBay Integrated Amplifiers, Amplifiers, Home Audio, Electronics. (end time 24-Jan-10 02:34:09 AEDST) They have 10k, 20k, 50k and 100k values available.

I will be feeding the power amps with the output of my soundcard RME(FF400) - it has selectable output levels that I intend to make use of to maintain best possible DA resolution while listening at low volumes:
0dBFS @ Hi Gain: +19dBu
0dBFS @ +4dBu: +13dBu
0dBFS @ -10dBV: +2dBV

Which value attenuators should I use?
Is there a minimum attenuation? I still want to be able to get maximum volume out of my amps if necessary.


Thanks

[AndrewT]

make the pot much less than the input impedance of the power amp.
If Power Rin=100k then 20k pot is suitable
Rin=50k then 10k pot.
Rin=10k then 2kpot.

Which of those DAC output options can drive which load resistance paralleled with some cable capacitance? I suspect none of them can properly drive 2k//500pF