changing the ohmage CAN change the tone of a
tube amp as it will load it differently. Don't forget the math. 2 speakers in parallel will be half the impedance of 1(never mix speaker impedance in a cabinet). i.e. 2 8
ohm speakers in parallel=4 ohms. Speakers in series will double. i.e. 2 8 ohm speakers in series=16 ohms. Check your amp to see if it has a max or minimum load. A 16 ohm load will net less wattage from the amp than an 8 ohm or 4 ohm load.(unless there is an impedance switch to compensate).