Did you paste the .so file in /Applications/AMPPS/php-5.3/lib/extensions/ext/ ?
How did you compile, can you give me the steps ?
Steps we follow are :
1. cd /<ext-source>
2. /Applications/AMPPS/php/bin/phpize
3. ./configure (with required options, you can take use --help for more options)
4. make
5. sudo make install
6. chown the .so to your user
7. copy it into /Applications/AMPPS/php-5.3/lib/extensions/ext/.
8. enable it from AMPPS -> PHP Tab -> PHP Extension
9. Restart Apache.
To check you can run the following command in terminal:
/Applications/AMPPS/php/bin/php -m