Any concerns about using a XLR to RCA adapter at my amplifier RCA input?

If you wanted to make sure, you could test the Neutrik adapter to see if the negative polarity pin is connected to the ground on the RCA adapter.  For a transformer coupled output, that should be the correct configuration.  You should have the configuration #6 on the following Rane wiring reference:

http://www.rane.com/note110.html

If you are using the following Neutrik adapter, there is a slight possibility that you may have some ground loop hum (since both pins 1 and 3 are connected to gound)

http://www.neutrik.com/en/accessories/circular-adapters/na2fpmm

If you do have ground loop hum, you may need to make your own cable/adapter and lift pin 1 from the RCA ground.

Looks like the VAC Preamp has a 8 volt output and the Audio Space AS 6M has an input sensitivity of 300 to 600mv ... seems the Pre my over drive the AS6M with it's 8 volt output or you won't be able to use much of the volume control on the VAC

This might be something else to take into account besides the PIN configuration that auxinput has brought up

You may want to consider a Pro Audio (XLR) to Consumer Audio (RCA) conversion box to knock down the voltage from the VAC to the AS6M

Here's one from Jenson ... http://www.jensen-transformers.com/product/pc-2xr/ ... a bit price at $329 but there are many that cost much less available on the internet