Thanks for the post. I'll do my best to answer in-line below. Please let me know if I miss anything!
> I'm interested in a passive attenuator device to put between my digital >source (dCs Elgar Plus, Purcell, Verdi) and amplifier (Jeff Rowland >302/4). The Elgar Plus has a digital volume control but it may not work >well in my setup, since I'll need a good amount of attenuation with the >high sensitivity of my speakers (VMPS RM/X, hopefully arriving soon).
I heard the RMX's atr CES last year and I am sure you'll have fun with them! I know the DCS stuff pretty well as I use a Verdi / Delius combo here myself. The direct connection can work well if that is your only source. The connection through the NOH is a tiny bit more laid back - which may suit some systems better then direct. It is very close (and one reason I chose the DCS stuff was to compare to a direct connection).
If it is the only source you have what I would do is get a couple of constant ratio reduction transformers to reduce the level. They could be made fully ballanced and would give you a nice impedance reduction as a result of the reduction ratio. That way you can run the level control up near the top where it is working in it's 'happy zone'. We can make these up with any ratio you'd need and I could package them nicely for you.
>I currently have a Sonic Frontiers Line3, which I've considered upgrading >to a SE+ by Parts Connexion at cost of about $1000. But it runs hot, >takes up two shelves, and I'd rather sell it and replace it with a simpler >device. Since I have a single source system all I need is a volume control > (with remote).
You answered my question from above about a single source system - I should read ahead.... If you think you'll add an analog source in the future then a diferent pre-amp would do the trick and the NOH should do fine in there.
>The Elgar Plus has output voltage switchable between 2v and 6v on both >RCA and XLRs. The unit is fully balanced by design, and other owners >and dCs folks have told me it sounds better balanced. Output impedance >for the XLRs is only 2 ohms, increasing to 52 ohms on the SE outputs.
Similar to my Delius (you lucky bugger with the Elgar!). I'd run the 6V out and reduce - although the 2V out would work fine as well.
>I know the NOH is available with XLR in/outs, is this a fully balanced >design or are the signals converted to SE internally? If the latter, could a >true balanced version be ordered?
The signals are NOT converted to SE inside. Transformers are inherently differential devices and when used SE they just have one side of the primary (or secondary) connected to ground. The transformers let you do SE - BAL conversion or Bal to SE conversion as well as SE/SE and BAL/ BAL connections. It is one reason I like trannies - they make the system options that allow system config and optimization easy to implement.
>Also what are the sonic differences between the silver and copper wire >versions?
Very close with the latest copper wire and leadouts. Search for descriptions but I recomend silver for fans of silver. Anyone on a budget (I am guessing from your system that is not a big concern) would be best served by copper. Call if we get to that and we can discuss it.
>Last, does the headphone option provide an actual headphone connector >or just an RCA output to hook a headphone amp to? With the low output >impedance of the Elgar Plus I would think it would have the cahones to >drive most pairs of phones. This was one of the things making me want >to keep/upgrade the Line3, it has a great built-in headphone amplifier.
It is just a switched (so it is out of the signal path) output that you connect to an outboard headphone amp. Lots of good choices for headphone amps if you sell your line3.
>Also considering a Placette RVC (resistive unit) and Sonic Euphoria PLC >(expensive with fully balanced option and remote control).
The Placette is a fine unit and the PLC looks great too. Both appear well made and I am sure wither one would work out very good for you.
If I were you I would do a constant ratio transformer and then use the built in level control. This'll give you great results and would be a nice clean hookup and be very user friendly. Ball park cost for a really good pair of constant ratio trannies (large nickel cores, etc) in a nice enclosure with premium connectors would be about $500.00.