the signal strength is at maximum, the reception is very poor and all stations sound very weak. .... no RDS data at all.

I have found that the signal strength often shows 7/7 but the reception is sketchy and the RDS is intermittent. If I can keep my eyes on the display long enough when this happens I sometimes notice the signal fluctuating between 6/7 - 7/7. I can get perfect reception and RDS data but it depends where I'm driving and what station I'm tuned into.

Silly question but have you tried driving about to see if you can get a good reception somewhere other than where you live?

In my case it's like the empeg needs a stronger signal than most HU's for the same performance and also the signal strength display is out of calibration.

My (15 yr old telescopic) antenna is worn out and doesn't stay up too well. I'm replacing it in a short while and hopefully that might improve reception, I'll post the outcome in here.