If you are in the USA, I would go for the 788T
If you are in the UK or mainland Europe, I would also consider the AETA 4MinX or Nagra VI (the 4MinX being about £2,000 cheaper than the Nagra and roughly on a par with the 664 price wise), both these are equal in quality to each other and equal or better than the 788T audio quality wise IMHO.