I just a/b'ed the nixon tubedac+ and the Ack! on a VERY outstanding system.....they are both excellent units, esp. for the $! ,but even w/o the $ consideration, they bested a couple very high dollar units. I, personally, prefered the Ack! by a wide margin. That battery power supply is a marvel. The blackest backround you'll ever (not) hear. Makes everything three dimensional. If you can live w/ the care and feeding nature of the beast, get it.
Oh, any digital cable by Mapleshade is super and if you can afford it, get the Omega Micro stuff.