The 604E-H, and the Altec Valencia/Flamenco woofer have a free air resonance of 25Hz. In the 5-6 cubic foot cabinet don't expect much below 50-60Hz. However in cabinets up to 12 cubic feet you can get quite good bass. IMO 9-12 cubic feet would be ideal.
With regards to the Valencias or Flamencos these sound pretty good at low volume but can get shrill and shouty, and the sound field gets muddled and collapses when pushed hard. Replacing the crossovers will help you get closer to what they are capable of. I've personally drilled the rivets, de-tarred them, reverse engineered the circuit, and build my own optimized N-800-F OEM crossovers...over a number of iterations. The stock crossovers have ferrite inductors next to each other, very old electrolytic caps, and an old variable resistor. Also, with used pairs its very common that they need new HF diaphragms or a LF driver rebuild both of which can be done for very reasonable prices at Great Plains Audio. I found one of my LF drivers was rubbing and had Bill @ GPA do them. He also remags Alnico magnets if he re-cones.
So, In short I don't think you can go wrong with either a 604, Valencia, or Flamenco. But either way you'll benefit from larger cabinets and better crossovers which is going to be the big value equalizer. The 604 are better near and mid field and the 2-way design might be better in a mid-large room.
