The Sonic Maximizer is not a crossover, it is a phase & amplitude aligner. BASICALLY, it takes the signal from your mixer & "realigns" the frequencies so they project better out of your speakers. For a better understanding on exactly what the Sonic Maximizer does
http://www.bbesound.com/technologies/BBE%5FHDS/ You can use it on vocals only, music only or the entire mix. I use mine on the entire mix.
The Peavey Kosmos is nothing like the BBE as it is more of a sound spatializer. It "creates" low frequency sound by analizing the original signal & generates a low harmonic frequency 1 octave below the original. It also has a stereo imaging feature which can give the illusion of a bigger sound. This unit also has a built in subwoofer output so it DOES kind of work like a crossover in the respect you can send your sub amp it's own sub frequency.
A crossover takes one signal & divides it into separate frequency signals so that particular frequency can be amplified. Crossovers can come in different configuartions as 2 way - splitting high & low frequencies, 3 way, dividing high, mid & low frequencies, 4 way dividing high, high mid, low mid, low frequencies. [/url]
The dbx 266XL compressor is a nice entry level unit. It will sound better than the stuff under it's price while still not breaking your budget.