I used to have the same combo a couple years back, but never ran into that issue.
Don’t remember whether that is the case, but have you checked, whether the pre has a gain setting? It could be that there is one, and it is set on a very low level.
If not, you’ve probably fried your amp. The thing is, the VX-5 Twenty is wired hot. That means, there is current on some of the the XLR pins when the amp is switched on. Therefore, if changing or adjusting cables when the amp is switched on, you’ll fry the power output stages.
I was using the combo with 88 db efficient Magico S3’s, and never came even close to running out of steam.
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