I dont understand what you just said...
but anyway, you can use a head or a rackmount pre/poweramp ( or both together... ).

if you just go rackmount ( randall modular for me ) you need both preamp ( like the marshall jmp-1 ) and a power amp ( like marshall 9100 ). sometimes the rack route is more expensive but it can also give way to new combinations of pre and power amp also with rack mounted effects it gives even more flexibility!
well i suppose it depends what you get but i definately prefer a cranked tube head sound to something that sounds like its been computerised to hell and sounds like youre playing a synth or something. just my 2 cents