I would suggest the
Antique Sound Lab Line Two DT, which uses one 12AU7 tube and costs $450.
A few years ago I used its predecessor model, the Line One, in my system while my main preamp was down. It performed very respectably, and of course its sonics can be significantly modified and tailored at modest cost by substituting different makes and vintages of the one tube.
The one caveat I would cite is that its output impedance is spec'd at 1,000 ohms, and most likely rises to significantly higher values than that in the deep bass region. Therefore, and taking into account your mention of the bottom octave as not being a concern, I would not recommend using it with a power amp or mixing board having an input impedance of less than around 25K, and preferably somewhat more.
Regarding driving the 8 speakers, assuming that you don't need to be able to control their volumes independently you might want to consider the possibility of connecting each of the two channels of a stereo amp to two paralleled pairs of two speakers in series. If each speaker is 8 ohms the amp would then see a load on each of the two channels of 8 ohms, although the maximum amount of power the amp could deliver to each speaker would be 1/4 of its rated maximum into 8 ohms. Also, for good sonics all of the speakers (especially the ones that are wired in series) should be identical models.
Good luck. Regards,
-- Al