I'd agree, don't go for freebies. You have good kit there that should be treated well. Having said that, I can heartily recommend the ThatCables sub £5 HDMI cables. They get 5 stars from WHF. I've got one and it's superb. Use that for Amp to TV and Source to Amp
The Sub and Interconnect cables need choosing more carefully as you've got analogue signals to think of. Maybe Van de Hul The Wave for Source to Amp depends on your source - what is your source? CD/DVD/Blu Ray make/model?
Sub cable: Could go up to a QED-Qunex SR, but might be overkill, a Chord Crimson sub could well suffice.
If you haven't already got them, you also need to consider speaker cables. Chord Carnival Silverscreen or maybe QED Silver Anniversary should do, for satellite speakers. You could look at something chunkier, but IMHO I'm not sure it's worth it for mini speakers.