Dean,
you probably are a great singer - so lay that aside. Different preamps sound different, just like mics. They have different eq plots. Ideally, they shouldn't, but there you go. However, these differences aren't blatent - in that one will sound great and the next like crap. Put different mics and preamps up and you are likely to get a reasonable facimile of whatever you are recording. Don't we all start out this way? And it works.
What works better is tailoring your equipment to the recording situation at hand. If you back off a dynamic mic through a mackie preamp, you might not get enough volume or too much noise. Do the same w/ an api (or GR or Sebatron) and it sounds just right. Same w/ what you are recording. A male voice in your example above might benefit from more low end in one song, but in the next busy mix some cut (w/o the nasel) might work better. If you are familiar w/ you tools and techniques you might choose the appropriate preamp. Or you could use eq, which works well, but we all know that capturing the right sound at the source is the best way and is the reason engineers get paid.
The SOS article/test was a good one, appolgies to Mike, in that it attempted to put all the preamps tested into a rather general and sterile recording situation. And guess what, all the equipment sounded fine. But didn't tell the whole story (see above).
For many, the cost of higher end stuff isn't justified by the returns. They might not be able to tell the difference between a built-in preamp and a gob-smacking one because their monitoring system doesn't really shine on the difference or the ears can't differentiate the difference or some other reason. But record the same song in a pro studio w/ a pro engineer and the home recordist will wonder why they can't sound like that.
But there isn't really a question to someone new to recording whether they should buy a typical interface or spend that money on a good preamp w/ no way to record it except through their on-board card. At the same time, there are plenty of home recordists w/o a bunch of outboard that do great sounding recordings. Better equipment won't have too great of an impact on their sound, tho I bet it makes it easier and quicker to get outstanding product. It is the ears that make the difference.
High end gear, used correctly, makes a difference. A small but decernable difference. The bigger difference is made by judgement augemented by experience. If you can't afford that mega buck channel, it doesn't mean you can't make good, in fact, great recordings. But it does give that last bit of shine and ease to production and allows you to make recording decisions based upon positive, not negative choices.
@