Of those two I'd almost certainly keep the Sanyo C55+ as well. JMO
Dont get me wrong I have plenty of love for NAD as well,but I much prefer my 106 preamps (own 2 now) to the earlier units.
The NAD 106 are big time sleepers,I mean how often can one find a sweet sounding preamp w/XLR outs for $100-$200 ?
The 106 was a later variant of the Monitor series 1000 preamp,between the 1000 & 106 was the 1000s,which also had XLR outs.
And a big positive for me is both the Sanyo C55+ and the NAD 106 can be rack mounted (FWIW I'm gonzo for rack mount gear,LOL).
I also have a NAD Monitor series stack as well (1300 pre / 2600 amp / 4300 tuner) as well as a 3140/2140 rig for my workbench system.
(all w/rack mounts of course...)
But the C55+ is a really sweet preamp for sure,and I really dig it's 1ru form factor.
They (Sanyo) sure packed a lotta goodness into that compact chassis.
When every rack space counts,that C55+ is definitely the unit to have on hand.
If I ever run across another nice C55+ within my price range I'll probably grab it just to have a back-up (IMHO they're THAT good).
But I digress for now...
Bret P.