The best coupling caps in power amp ?? Mundorf, Infinicap ??

Mundorf are excellent caps.  M-cap supreme, great in midrange, very rounded sound.  The silver has better clarity, more tranparent.  The infini-caps are neutral, kind of forward sounding.  Very analytical sounding caps, nothing really interesting about it.   Go with Mundorf caps, you will be happy with it. 

I placed Jupiter copper foil caps in my 300b SET (replacing the stock Solens) and it's a worthwhile upgrade.  I went with them rather than the Duelund CAST due to the lower cost and enthusiastic recommendations. 

The Duelund CAST is superb in my DAC  and speaker  crossover (tweeter).  Though expensive I believe they are definitely worth their cost. 
Charles 

I would agree with your assessment of the Infini-caps, but I have some interest in maybe using Mundorfs.....I think I will read on about other experiences

Two very experienced modifiers on this site Grannyring and salectric seen to prefer the Jupiter copper foil compared with the Mundorfs. 
Charles 

If price is not an issue then i would go with the jupiter copper foil.   That is comparing the Mundorf and Jupitor.  If space permits, i would get the Duelund cast hybrid.