It has been posed a few times and the question should get a fairly thorough answer....

I just bought a HL/Taigen airsoft tank. How do I modify it to get it to do <XXXXXX>.

1. Recoil?
   
2. Better Sound?
   
3. IR Battle capability?
   

Recoil
In general, unless you have a newer Taigen version that has a combined airsoft/recoil mechanism (Last I checked they were still testing the Tiger prototype), you will be forced to modify and install a dedicated or kit bashed recoil system. The issue becomes how can one control the recoil unit? Most aftermarket units and kit-bashed units are driven by a servo. This usually requires a change to the Main Function Control board (Converting to Clark/IBU/etc. aftermarket boards). These new boards range from $100-$300+ CDN and do require extensive rewiring and setup to function.

Better Sound
Louder or more realistic? Louder is fairly simple, add in a small amplifier and a better speaker. Otherwise, use an aftermarket control board that either has better pre-loaded sound files, or customizable sound files.

IR Battle Capability
The simple method? Buy a Tamiya IR Tank. Buy a Tamiya receiver (Apple).
The cheap method? If you already have an IR tank (Non-Airsoft),  buy an aftermarket IR board such as RCTA Mako and install it in your HL. However do not expect great performance as the receiver (apples)/emitters are not great...
The custom method (Popular). Buy an aftermarket control board that replicates the Tamiya Battle system. Buy an apple. Complete re-wiring and modifications...

first you need to let it sit on a shelf for 2 or more years . . . . . . . . no wait thats just me

You have to make sure it is in all its component pieces before you put it on the shelf. So you have no idea how it goes back together.             That may be just me......

Shoveler74 wrote:

You have to make sure it is in all its component pieces before you put it on the shelf. So you have no idea how it goes back together.             That may be just me......

I have the component part down part anyways!