The T100S output:85w per ch -> 4 ohm50w per ch -> 8 ohm (which I assume the split stacks are)25w per ch -> 16 ohmThey have 3 tubes per chan, 1 12AX7 driver (phase splitter) and 2 6CA7 (=EL34) power tubes
This should
much louder than the 5w blackstar (double the volume takes 10 x the power ie 50w vs 5w). In your case you have 2 x 50w so add 3db to twice as loud. However, as the T100S input is just one 12AX7 phase splitter you need to drive it pretty hard as there is no additional gain at its input.
The lead you need for the cab sim/phones output is a standard stereo to double mono shielded lead (there's a wiring diagram in the B* manual showing the stereo end). They are more commonly known as insert leads as that is what you use in the insert jacks on mixer channels.
I used a HT5 once for a soft rehearsal, nice amp, the reverb is very good BTW but the amp is not very loud and cant compete with drums. I have a Carvin TS100 which is a modern equivalent of the T100S. It competes with drums no problem and then some
. The speaker emulation is fine if you want to record or go into a desk live. This is basically what the HT5 is designed for.
Recently we started to use my split stacks that had been sitting for a few years and the jacks were dirty and causing issues.