Please help me see what I should be looking for. I would like to acquire activity
based Remote Control. My home theater consists of:
AVR - Harman Kardon AVR235
DVD Player - Harman Kardon DVD-22
Plasma TV - Philips 42PF5320
Subwoofer - Velodyne SPL1200R with remote control

Any suggestions will be appreciated!

Please advice also whether the activity based remotes allow also to learn/use the individual and more subtle functions of the home theater devices.

Budget?

I'd reccomend URC's MX-850. PC programmable with a huge database of codes, and fully learning for anything not already in the database. The database has many discrete, or "advanced" codes that your OEM remote might not have (such as "on" and "off" instead of "power," "input 1", "input 2", etc. instead of a single "source" button...)

Thank you very much but the price of the URC's MX-850 seems too high for my needs. Furthermore, all the devices I have are only IR based while MX-850 has also RF. Will appreciate other options that are more budget oriented.

Have a look at a Harmony 550