I also have a Reference 150, so this is of interest to me. In the ARC amps I'm familiar with, the resistor that blows is in the path that supplies bias voltage to the tubes. What usually triggers the resistor to blow is an internal arc or short within a tube, which in turn generates a big current spike through the resistor, causing it to blow. I've also heard that this is a protection mechanism that ARC uses in place of fuses in the signal path. The damage is generally limited to the bad tube and the resistor.
However, looking at the photo here, the resistors that have blown are very small ones and I'm not sure they look like the resistors in the bias path. The Reference 150 could be using some other kind of protection circuit that I'm not familiar with. It would be nice to have a schematic diagram of the amplifier for troubleshooting purposes, but as far as I know, ARC doesn't release those to customers.
To be safe, you should not turn on the amp again until it's fixed.
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