Help needed running two heads to boost output power and control highs/lows

[OldManBassDude]

Hello! I am new to this forum, and am in need of some input please. I really am an old dude. I started out as a drummer back in the day - I've played trumpet too - but have been playing bass for almost 40 years now. Here is my quest:

I have a Yamaha 300 watt PA mixer head that I want to run into a 500 watt Peavey power head that is bi-amp with a built-in crossover, four speaker outs, two highs, and two lows.

I want to boost the output power a little, and be able to separate and control the highs and lows. I have the speaker cabinets to do so. My question is, how do I run one head into the other without blowing them up? Should I go from the Yamaha into the Peavey with
1. Line out to line in?
2. Line out to mike in?
3. Speaker out to line in? or
4. Speaker out to mike in?

Any advise will be greatly appreciated. Thanks! The Old Man Bass Dude

[DWBass]

You can't boost the power. You can use the pre-amp section of one into the other but you can't hook up 2 amps together in an effort to increase power. What model PA and Bass amps do you own?

[OldManBassDude]

The Yamaha is an EMX660 and the Peavey is a MegaBass digital. The reason I want to run the Yamaha through the Peavey is so that I can use the bi-amp capabilities to separate the lows and the highs. The power is not that important. I just don't want to ruin either piece of equipment in the process.

[MuzikMan]

Line out to line in. Don't try speaker out to line in please.

[OldManBassDude]

That's what I thought, but I wasn't 100% sure. Sometimes, after having been down the street and around the block more than a few times makes it difficult to remember. Thanks!