Amplifier for rear channels

Unless you rear speakers are more than cubes I wouldn't bother with upgrading the amplification for them.

I have "junk" rear channels in my 4.1 system and I have never noticed them lacking for movies. Even when listening to surround SACDs I don't notice a deficiency unless the recording is centered in the music. I have a LAGQ SACD that places each guitar in a different speaker and it obviously doesn't work with my Focals opposite the "junk" rears.

I would consider putting the money toward something else.

If you're talking about going 7.1 then there may be some gains, but I'm a big fan of 4.1 or 5.1 over 7.1 unless you have a dedicated room for movies. I just don't think it makes that much difference to the movie experience where visuals distract quite well.

Who made your front and center receiver /amp? For sound continuity you may be able to get a 2 channel power amp by the same manufacturer. Which speakers are you using?

I am using RF-7, RC-7 DeanG and RS-7. Ampilier is a BAT-VK-6200

That BAT is an expensive amp, but you sure don't need to spend that kind of money to dabble in 7.1. Keeping at the 200 wpc, Outlaw Audio's mono block, the 2200, is 679 for a pair. Outlaw is a well regarded internet direct manufacturer, as is Emotiva. Their options include the XPA-100 which is another mono block, about 600 for a pair. They have some 2 channel amps, but are either less than 200 wpc or more.

Parasound is another good option, but has the traditional dealer network and costs more. Audioadavisor.com has a demo model of the 2250(2 channel amp) for 1188, or a 'factory refreshed' unit for 999. Just some options for ordering online. If you prefer going into see a dealer, you'll spend a good deal more I suspect.