The Altec duplex used in the early UREI monitors is the 604-8G, but the horn is different and the crossover is not Altec but UREI and is time aligned. I've not heard them (though I'm very familiar with the stock unit), but what I wanted to say is I'm also very familiar with the Tannoy SGM10B and the Manley Labs version which uses the same coax unit with a time aligned crossover. It definitely matters. Although the value of time alignment is sometimes debated, I think in a coaxial driver it is unquestionably a worthwhile improvement.