IPA/XSAMPA help - what am I saying?

I've become badly confused by the IPA sound page I've been using
(http://www.ling.hf.ntnu.no/ipa/full/), and the English pronunciation
threads I've been reading here. I've put up a few samples of myself
speaking; can someone listen to them and tell me what the XSAMPA
and/or IPA for these vowel sounds are?

  http://sniff.numachi.com/~rickheit/words.mp3
  http://sniff.numachi.com/~rickheit/words.wav

(please reply to me, not to the list - I'll summarize any results)
These are all vowels in my normal accent, a New England rural accent
severely influenced by a lifetime of TV and movies in American
Standard.

In general, I was hoping for an explanation of the usual vowel
chart. The chart implies that, modulo pitch and volume, a vowel
sound can be described with three variables: roundedness, openness,
and frontness. Is this so?  Could one build a vowel generator, where
you pointed to a spot in the chart and got the vowel sound there?
Could you numerically describe a vowel sound with any accuracy?
("The average Italian 'o' is (+0.83, +0.27), with a range of 0.1
front or back considered acceptable") Or is this chart just a
covenient way of writing things on a page, and the identity of the
sounds subjective?

        Erich