As long as your ipod has a line out with volume control, that's all you'll need. Or, if it has line out but no control, you can use something like the NHT or ATTY to attenuate the level. I'm not an audiophile, but don't know iPod!
Now most McIntosh have level (sensitivity) controls, but they are typically two separate knobs and that would probably be a pain to use for continuous volume settings.
Most of the tube McIntosh can be a little pricey. I have the MC225, they often go for $1500-$3000 or more, depending on condition. MC240 probably around the same. These are lower wattage (rated 25 and 40 wpc, but measure higher), but sound so incredibly sweet, especially the 225.
Here's the standard resource for information: www.roger-russell.com
Good place to buy and learn: www.audioclassics.com
Good shop, they refurbish and sell nice working products, and specialize in McIntosh.
And another place that refurbs and sells them, no personal experience with them: www.mcintoshaudio.com/
Best luck, they are beautiful amplifiers. Of course, there are plenty of other cheaper tube amps as well.