See is in the present tense Seen was used because the "playing in the band" had already happened In the second example...... To "see" him the context would be the present tense ........I see him playing in the band // Or: I will be excited to "see" him play in the future

I don't really know how to explain specific grammar rules that well but I'd say it's because there's the present perfect 'have' in the sentence. If it were just 'would' and not 'would've (would have)', it would be 'Would much rather see him', but because it's 'would've' then the past tense, 'seen', is used :) e.g. I have gone there --> l would have gone there I have bought that --> I would have bought that I have seen him --> I would have seen him etc etc Hope this made sense and if it did, hope it helped!

Would have is a past modal verb. Past modal verbs are followed by the verb in the past participle. Other past modal verbs are could have should have might have