adding keyless push start

Here is a picture of my button installed in my TT G35 coupe:

My system currently uses the OEM keyfob for locking and unlocking and then uses a passive RFID system to authenticate the system for keyless starting and operation.  I completely bypassed the steering wheel lock.

You need to be careful how you go about doing this - and for my personal situation this is what worked for me.  If you go with a fully active system and eliminate the ignition key cylinder you are putting a lot of faith in a lot of things that you will be able to start your car up.  OEM systems have built in fail safes, something that aftermarket systems can't duplicate.  I would never recomend someone replace their ignition switch with a push button - the chances of not being able to start the car (especially with an active system) are way too high.  You're just asking to be stranded somewhere because either your keyfob broke or the battery in it died.

My car can operate completely with the key or completely without the key so I never have to worry about the car not starting if something in the pushbutton system quits working.

There are some vidoes on YouTube of my system in action - do a search for "Keyless G35 pushbutton start "

Just curious, what didn't you like about the Digital Guard Dawg?  They are expensive, but their technology is pretty impressive and I've read nothing but good things about them (or at least their anti theft products).  Their pushbutton system looks a little "rough".