"The wrap on several caps swelled..."
I'm not sure that several of the caps swelling at once is necessarily an indicator of a general reliability problem with the board. I wonder if something else is amiss that might have caused a catastrophic failure?
I think there are a few considerations here. Going with the quad section cap is, of course, a fine option.
However, if you go with the newer kind of quad cap with the even higher voltage rating, be aware that it has discrete electrolytics inside, but does anyone recall how they are arranged? In other words, in order to achieve the higher voltage ratings, does it have electrolytics in series inside the quad can? If so, then you’re really no better off reliability-wise than using the cap board. At least with the cap board you know you can have resistors across the electrolytics in an attempt to equalize the voltage – does anyone know if the electrolytics in the quad can have voltage equalizing resistors? OTOH, if there are only four discrete electrolytics inside this newer style can, this would not be a concern, but I’d sure want to find out.
Alternatively, if you use the traditional style quad can that’s built like a Swiss roll on the inside, then you’re going to have higher ESR and also a lower temperature rating (55C, IIRC) that seems a bit on the low side for this application. Not that the Swiss roll style wouldn’t work well enough, but I think the higher temperature ratings of the low ESR electrolytics and related features of the cap board provide an overall performance advantage. The increased capacitance alone of the cap board is likely an advantage over both kinds of the quad cans.
There was more than one cap board that Triode USA was selling. One was the original Sheldon Stokes board while the other is somewhat different, which Triode calls their “Upgrade Capacitor Board.” This second board is the one they appear to be selling now. Which one do you have, the original board by Sheldon Stokes or the Triode USA Upgrade Capacitor Board?
I am not very familiar with the original SDS labs board, but I have the Triode USA Upgrade cap board in my Stereo 70. One thing I did do was to calculate different resistor values for the series resistor pairs in parallel with the electrolytic pairs. The original values are okay for bleeding the supply when the amp is shut down but do not do much for protecting the electrolytic pairs in operation. I reduced the values of these resistors so that they draw roughly double the maximum leakage current of the electrolytics. This could add some protection as the capacitors age.
But, in your case, it does seem kind of suspicious that you had your meltdown coinciding with the tube changes. You might not want to write-off the cap board too quickly, especially since you like the way the amp was performing before the meltdown. As far as the voltage ratings of the last three sections on the Triode Upgrade cap board, each one of those electrolytics is rated for 250 working volts but typically have a 300V surge rating, which means each of the last three sections actually have a surge rating of 600VDC.
So, IMO the quad can is a fine choice and also the easier choice. Although the cap board is more of an involved affair, I think it can offer a performance advantage while I would not think it should have to be serviced regularly under normal circumstances, though I would want to reduce the value of the resistors in parallel with the electrolytics.
In the meanwhile, I’d consider other possible reasons for your cap board’s failure. Did your AC line voltage spike? Maybe there is an issue with the tubes...?