Hi ALL; I have a SONY power amplifier but I need a MAX5406 chip ( the only one I know ) to get it working.
I understand its obsolete but I dont care. I need to source one, or something similar in USA; can someone help? Thanks.
I doubt you'll find a drop-in replacement. You'd probably have to re-build the entire preamp section. That wouldn't be economical or practical compared to the cost of a new amplifier or receiver. (Stereo receivers or home theater receivers are usually more economical than amplifiers because receivers are mass produced & competitively marketed.)
If you could find another bad amplifier of the same (or similar) model you might be able to salvage the part. (Usually the power-amplifier section blows first, so the other one probably wouldn't have the same problem.) ...But, if you find one at all (on eBay, etc.) you are more-likely to find someone selling a working one than a non-working one. 
I have a SONY power amplifier
It this has the MAX chip it's an "integrated amplifier" with a preamp/control section and power amplifier built-into one box.
A [u]power amplifier[/u] is "just an amplifier" that boosts a line-level signal to speaker-level. Some power amplifiers just have one input (or a stereo pair of inputs) and sometimes don't have any controls. Sometimes there is a volume/level control and some newer power amps have DSP processing (EQ etc.) but the controls are for set-up and configuration and the preamp (or something else) is used for everyday volume control and input switching, etc.
A receiver is a power amp, preamp, and radio tuner in one box (sometimes with HDMI video inputs/outputs).
Or you could actually search for one and find a source:
http://comelec.fr/index.php?id_product=5816&controller=product
or https://www.ebay.co.uk/itm/MAX5406-Integrated-Circuit-MAKE-Maxim/163256231565?epid=1248427679&hash=item2602d4668d:g:720AAOSwxMRbmpoB:rk:1:pf:0