I think you may be confusing H-alpha filters for solar imaging and H-alpha filters for deep-sky. They are completely different animals.
A deep-sky filter (of which the clip-in is an example) has a bandwidth of around 5-15nm and lives at the camera end of the imaging train. It is designed to pass the
light emitted by H-alpha in a dark background.
The solar H-alpha filter (system) consists of two parts and has an extremely narrow bandwidth (<0.1nm) and is generally a dedicated telescope.
As you have seen, it's quite common to replace the IR filter in the camera. Different cameras have different levels of response to Ha. Some DSLRs might be a
stop or two down but some like the 5D2 seem to really knock it out. If your camera isn't sensitive to Ha, adding an Ha filter isn't going to help. However, if you live in a region with lots of
light pollution, a
Light Pollution filter (LP or CLS) will help a lot as it blocks streetlight wavelengths and passes astronomical wavelengths of interest so you can expose for longer before the background washes out your subject. You can buy those as either eyepiece filters or clip-in filters.
Of far more importance in astrophotography is the mount. Where every other forum will say "spend your money on good glass", here it's all about the mount. Any form of equatorial mount will open up a universe (pun intended) of possibilities. That can be as simple as a homemade barndoor tracker upwards. Then it becomes a case of staying within the capabilities of the mount.
Steve.