I am a little confused on your post you talk about R17 and the triode at the same time R17 is the cathode resistor for the EL84. I am trying to check what I had as a final value and it looks like 270 ohms, but it is best to use a voltmeter and check plate voltage and cathode voltage to calculate the power dissipated by the tube when making these changes. Not sure I covered amplifier output tube bias in this thread if you go to Sewatt on the Valve Jr page you can find it there. If you do parallel R17 to get say 270 ohms with a 1.5k the 1.5k can be a 1 to 2 watt resistor.
On the bass response end one big limit to the stock bass response of the amplifier was the capacitor values used in the op amp circuit, you now have that bypassed. I know I posted what I found for bass response and it is as good as it gets on this amp especially with the 20:1 turns ratio and an 8 ohm speaker. So even if you changed the output transformer I doubt you would do much better.