How to connects 2 amps highs and lows hi end

You need a separate crossover. Use one amp the B and K is a good amp for both highs and lows.

If the Snell E4 are set up with 2 pair of inputs on each with a connection between the 2 red and 2 black terminals then you would remove that connection and hook up the bass amp to the woofer +/- and the treble amp to the tweeter +/-. At the preamp you would feed both amps from the main outs. You might need y adapters if you don't have more than one pair.
You could do this but I would suggest that it will not be work the effort. It would also be very easy to blow up the tweeters.

Are the Snells BiAmpable? If not then you would need an outboard crossover unit. Not worth the time or effort. If you're not sure,bi-amiable speakers have a set of brass colored bridging bars where the speaker wires hook up to them. To Bi amp them you remove the bars and hook up one amp to the hi pass and one amp to the low pass. Of course you still have to contend with the problem of connecting both amps to the preamp.

The Snells are quite efficient and will not benefit by using 2 amps. It would make more sense to upgrade your electronics rather than add an additional amp.

Bi-amping or tri-amping is always better.
Using an electronic crossover (required) you are able to control the crossover frequency and loudness of high (mid) low separately.
This is a huge advantage over "built in" passive speaker crossovers. It will allow you to get more (or the most) out of any given speakers.
It will make any speaker sound better, clearer, cleaner. It will allow you to protect the tweeters, etc, from the wrong frequencies.
Once you have run your system biamp / triamp, you will never go back to the old way.
(FYI all professional high quality systems are biamp triamp....etc... Consumer grade systems are not.)

AND if you should have time correction (digital delay, etc...), on the crossover, this is even better.

The deal goes like this:
Source, CD....>preamp>EQ>crossover> Low freq amp> woofer(s) in 3 way systems, very often the lows are run in mono, and it works very well
> High Freq Amp> tweeters whatever

However a better system would be:
Source, CD> Preamp > EQ > Crossover > Compressor Limiter > Low Frequency Amp > Woofers in mono
> Compressor Limiter > Mid Frequency Amp > Speakers in stereo
> Compressor Limiter > High Frequency Amp > Tweets in stereo
And this type of setup would be ultimate for home hi fi.
Of course, you guys gotta whine about EQ, Digital time correction, Mono woofers, compressor limiters...but you are actually missing out by not using them.
And you will never realize what you are missing, until you actually try it.

Oh yes, I have built systems up to six way. Powered by 22,500 watts RMS. But you don't need quite that much for hi fi.