I bought the 2 books and am a new Hookpad+ user I must say you've got a great system.
I often want to lookup theorytabs on my mobile devices for referencing what I listen to. As you know I get the "you need flash" warning and can't access any of the theorytabs content unless I'm on a computer.
It would be great if you would be able to bridge the database content to visually display a snapshot (no audio, no playback) of the theorytab in a platform-agnostic non-flash format for browsers that don't support flash. The way it would work is users would see an image-only version of the theorytab when the page loads (page would probably load much faster too) and when they click on it it would load the flash version for playback. Or similar to how websites have a mobile version with a link on the bottom of every page "view mobile version" or "view desktop version" you could use browser recognition to decide what version users will see by default first.
I think it would improve your customer acquisition tenfolds as more people could potentially access all the free content your are already providing and it would probably improve the sales conversion rate from new visitors as they'd perceive you provide more value to them and they'd spend more time into your ecosystem and more time spent mean they're more likely to purchase sooner or later.
We actually did use to display a static image and I honestly have forgotten why we stopped doing that.
Either way, we're going to do one better. As you problem know, we recently released a completely new version of Hookpad that doesn't require flash. Our plan is to do the same with Theorytabs and it's our current top priority for exactly the reasons you mention. Should be live on the site in a month or two (but don't hold me to that )