I talked to Patrick533 and he was very helpfull, thanks. He's suggested and I've bought PL-APN that has 1W radio, configured it as AP in a bridge mode and wired it to DIR-657. Disabled the wireless on dir-657. The wiFi signal strenght is very good throughout the house and the wireless connection is much more stable. Dir-657 works very solid now. The only problem I have is PL-APN droping off the internet and requiring rebooting every couple of days. The wireless connection between the PCs and TVs (supported by PL-APN) doesn't drop though, just the internet gets lost. It seems to be a problem with PL-APN only because the PCs wired directly to DIR-657 don't loose internet connectivity. In general my home networks is much more stable now but still not perfect.
