TVC with subwoof or cdp direct to amp & sub

I am intereseted in using a transformer based volume control or a CDP that allow direct connection to amp. Are there any problems with the addition of a velodyne DD12 sub.

My amp has 100K Ohms input impedance. I can't find input impedance of the amp of velodyne sub.

When using a line level input, would CDP or TVC provide insufficent voltage to the amp if sub-amp is shunting current from the amp?

I think i can circumvent this by using speaker level input but line level connection seems to make more sense. (Using sub with speaker level input may require more internal processing.)
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I'm using an Audio Zone PRE-T1 TVC which has two sets of outputs. Highly recommended. BTW, how is the ASL 1009 working out for you?