If you are sold on the single driver design, I would stick with the folded horn for the box. Check out The Hornshoppe, Jericho horn or ZHorn (there are many others). The Pi Studio Series 2 Tower will give you good bass extension without and have no XO (like a single driver) and are priced in a way that is hard to beat.As far as less sensitive speakers, the EL34 amps that have more power than SET's are very popular with tube listeners and even with more sensitive speakers like horns (even folded horns).