Can't drive Proac Studio 110 with low budget amps

First I'd try moving the speakers closer to walls and reflecting surfaces, which may re-inforce bass. Secondly, these speakers deserve better amplification than some mid-fi receiver. Try a seperate power amp. You should be able to get by with at least 100 wpc. Remember, a 100 wpc amp will sound very different than a 100 wpc 7X100 AV receiver. My 100 wpc amp weighs in at 85 pounds, it has a much stiffer power supply than any receiver, and does not run out of steam when pushed.
200 wpc may do even better for the ProAcs.

Thats what I am going to do: find a powerful amp for a test. One thing that confuses me a lot is the fact that several people told me their 50 watt amps can drive Proacs pretty well (Audiolab,Naim,Arcam). Also, placement is not an issue here, I can see that the woofer is barely moving when it is supposed to really do a hard job.

With a lot of speakers it is not so much the raw power available, like for example 200wts at 8 ohms, as it is the current delivery to speakers with lower impedences i.e. 4 ohms and below. Amps which double power output at 8 ohms when it droops to 4 ohms or lower, are a good candidate for success. Those which do not may well have difficulty driving your Proac's I suspect (I've never seen the actual impedence curve of your speakers).

Re raw power - 50wt amps which double from 8 to 4 ohms will sound more powerful than their actual wattage suggests especially if your speakers have an efficiency of 90+db. If you don't listen to them excessively loud in a medium size room you could probably drive speakers with a 86db efficiency. I've used an loved high current 50wt amps with 86 db speakers with difficult impedence curves in a medium size room.

FWIW, I've never had Proac's in my home.