mail arrives as attachment, not as html. (need template, theme guidance, too.)

First, let me say that I hate posting things like this in the issue queue, but I can't find a better place to ask my questions. I've been trying to get htmlmail (and simplenews) to work for a good bit of time, and I keep running into dead ends. It seems to me that there's a lot of interaction between various modules and that's making it very hard for me to reproduce each error circumstance when it happens. That said, here's my problem.

Goal: an HTML newsletter with images, etc. possibly with some dynamic block content from the theme.

Drupal 6 platform, with modules:

• htmlmail(6.x-2.61)
• echo(6.x-1.7)
• mailmime(6.x-2.15)
• emogrifier(6.x-1.17)
• pathologic(6.x-3.4)
• simplenews(6.x-2.0-alpha2)

I've made a simple theme as a subtheme of my site's theme to kill extra regions and content blocks and make the HTML as simple as possible.
I copied the htmlmail-simplenews.tpl.php into the new theme directory as htmlmail-simplenews-test.tpl.php.
I built an input filter that applies (in order):

1. line break converter
2. URL filter
3. image filter
4. inline images
5. inline contents
6. link node filter
7. video filter
8. emogrifier
9. pathologic

I've configured htmlmail to use my new theme and input filter.

The result is that my text content was correctly marked up and displayed, but images in content didn't come through, although the logo image in the theme does. (the logo image the template does not). The odd thing is that when I switch from my theme to "none," The images in content came through just fine, but of course I have no theme.

Images in content are inserted as img_assist tags, like this:

[img_assist|nid=966|title=|desc=|link=none|align=right|width=320|height=266]

I've been fiddling with mimemail, htmlmail, and other settings to figure out what's going on, but I'm not getting anywhere.

This evening, there was a development that caused me to write this. Now when I send test newsletters, or use the "send test" function of HTML Mail, I end up with an email with an unnamed MIME attachment instead the actual HTML in the mail. The attachment does contain the HTML text, but I'm still missing images.

I'm really not sure where I've gone wrong, but I feel like I'm just tying myself up in knots at this point. I hate to just throw my hands up and ask for help like this, but I'm afraid I need it. Where have I gone wrong? What should this really look like?

I can boil my problem down to two questions (I think):

1. How do I get a template and a theme to play well with each other and display images
2. Why is my HTML showing up as an unnamed attachment instead of appearing in my message body?

Thanks for listening