you should have no problem running two 8 ohm spkrs in parallel which would give a combined 4 ohm load..there are very few amps today that would have trouble at 4 ohms. whether you use 2 amps is up to your budget. One side effect of using 2 spkrs is a smearing of the imaging which you may or may not like..it would be more pin point with one spkr I'm assuming centrally placed over the tube..with 2 spread apart between the main L & R the image will be more dispersed