Tube amps have output transformers and their secondaries (the portion that connects to your speakers) can be electrically represented by a series inductance. If you then connect high capacitance cables to this inductance, you effectively produce a low-pass filter. This would mean that your highs would be a little rolled off but it shouldn't affect the bass. Technically speaking.
However, many of us have witnessed that the impact of cables is much more complicated than that. Our ears can hear more than we can measure. As a result, the only good way to find the right cables is to try several and pick the ones you liked best. The explanation for why they are the best will not be clear - everyone will have opinions but no one will have proof. Lucky for us, the outcome of experimentation will be sufficient for great sound. Good luck!