setting up ABX tests at home

I want to set up an ABX test at home on different sources to see if I
can hear a difference. I am doing this for my own education and fun -
I don't want to start investing in SPL meters, switches gain
equalizers of other boxes.

The sources are a Panasonic discman, an arcam CD player a squeezebox,
and hopefully we will borrow a high end CD as well. I will obviously
do it in pairs. I will have a helper switch manually. All units can be
connected to my budget level integrated NAD 325 BEE and have a copy of
the same media source.

My problem is how to neutralize differences in volume without
investing in equipment I have no need for. I can think of four
strategies

1) For each test start with volume at 0 and have testers ask for
volume to be adjusted to level they like.

2) Have the helper randomly set volume each time

3) (Maybe) use a PC to measure volume - not sure how to do this but I
do have a cheap microphone and audacity on the PC which should show me
the volume level - I don't know how accurate this is.

Advice appreciated.

Steve