Del, if you actually meant to refer to the Sennheiser 280 for a closed-back phone, that would be a fine choice for situations where you had to use a closed phone. I also prefer an open-backed phone for use whenever it's possible and would suggest you consider the Sennheiser 595, excellent and considerably less than the 650. Possibly the best source for reliability and price for the
280 and
595 is J&R.
As to the cable, as Ken says, unless the included one is damaged and doesn't supply a stable connection, there's no good reason to replace it and this wouldn't actually be an "upgrade". A very thick replacement cable would have lower resistance and might be slightly louder at the same setting, giving the misimpression of better sound and leading to some of the stories we read about.