Internal Speaker Cabling

Yes! Upgrade internal speaker wiring. Madisound indicates the use of Nordost Flatline (rectangular conductors, teflon dialectric), my friend made kit speakers with this wire and they sound more alive/spacious than the same speakers I made with Audioquest Indigo Litz.
Avoid usage of thick, hard to manipulate cable, sucks to work with in enclosures. I have seen the inside of dynaudio speakers (contour/evidence)..that use 12ga zip cord! Due to all the oxygen which can penetrate stranded cheap zip cord..I have seen this wire turn green (oxidize) in 5 yrs.
The best cable I have tried has always been solid core conductors (rectangular or round) with teflon insulation. Exotic arrangements of conductors (litz) don't seem to really improve sonics that much.
I suppose your only concern here is, that speaker designers voiced their designs with whatever wiring they used..so using different wire could throw off their initial voicing. However..if dynaudio uses zipcord..you can discount their engineers belief/understanding of the effects of wiring. Their speakers sound dry and lifless anyway.

Another way to view this ..is the fact that only a couple feet of wire is used internally, so it dosen't matter as much as the much longer run of external speaker wire.
A funny fact: when I (and others I know) used to use 12ga zip cord for speaker cable years ago..we would occasionally hear police radio transmissions through our systems as a cop car drove by. The idea being..zipcord is 2 parallel unshielded conductors..which acts like a RF antenna, especially when run in a straight 10-20 foot line.
Nrchy: I know manufacturers pay attention to the internal wiring, I simply feel that some pay more attention than others..and I know there are engineers/enthusiasts who say that fancy speaker cabling is all hogwash. These are usually older people who have fixated ideas of what is and what is not..and their hearing is rolled off due to age, so they'll never hear the difference anyway. Oh yeah...and some of those are the same people who design speakers and have wrong opinions about wire.