digital or analog volume control?

You may want to check with the person who is doing the modification.  If he places the volume control before the line stage, then you are good.  The line stage will have its own gain and voltage to drive the input impedance of the amplifier.

Thank you.  Actually the dac is a monarchy audio M24 which is a dac and a linestage/active preamp  combined.  The modifications will be to both the dac and the linestage, so if I don't add the volume control (the original volume control will be removed no matter what I choose because  it was very poor quality) I will essentially have an active preamp with no volume control feeding my amp.  Not sure if that makes a difference. 

I have gold plated connectors that pass GHz signals cleanly. Gold plate does not roll off highs.

But on your placette passive, the extra cable could definitely affect how clean the sound was, especially if you are using copper cables with gold-plated RCA/XLR (gold-plated will warm the sound and roll off the highs).

If you are happy with the performance of the digital volume output, then just continue to use that.  If you want a good analog volume, maybe look into an active preamp.  That can get expensive for something decent and it will also effect the sonic signature somewhat (but not necessarily in a bad way).

auxinput, thank you.  I wasn't aware that adding a volume control could affect the output impedance of the source.  This makes sense though because I ran my system with a placette passive in the chain and when I removed it and went back to the direct connection with the digital volume control it was like someone took 3 blankets off my speakers.  I always assumed that was because of the additional interconnect introduced into the chain, but perhaps it was because of the impedance difference cased by the passive itself.  If that was the case I would most definitely favor no volume control, especially since it will be built in to the chassis of the dac itself and I will not be able to do a comparison before I make the decision.   

If you decide to go with an ALPS have your tech check out this...

https://www.partsconnexion.com/ANVPOT-81914.html

Only available in 100K Ohm though, as far as I know.

DeKay

There is controversy in this industrial as to whether a digital volume is just as good as analog volume control.  At 32 bits, most engineers say it doesn't matter.  I have always been of the opinion that digital volume can be compromise, especially at low listening levels.

That being said, adding an analog volume control to your output could affect the output impedance driving the amplifier.  You are, essentially, placing a "passive preamp" between the DAC and the amp.

Buffered or unbuffered volume control, and if buffered, what circuitry is forming the buffer for the amplifier?