Lucky you! Piano lacquer... I can only dream. I'd be paranoid about fingerprints though.
Yes, when I first got the Ren 90s I used only my 555 - it didn't work well at all. There was almost no bass whatsoever; although I think that may be a crossover issue. I wouldn't call what it did produce grainy at all, but I can't really judge the mid/high tonal balance without any bass...
Now I run them with the 555 just for the woofers; it provides ample power and control. I can't even remember if I've ever lit up the distortion lights on it.
Up top I run a Carver TFM-15CB. It works great, has enough power in medium sized rooms to avoid getting anywhere near maximum output (and clipping), and best of all it has gain controls so you can adjust the relative level of the mids/highs with the bass. Without gain controls, if you biamp you have to carefully match the gain of your amps or have another way of controlling their relative volume (a multichannel receiver should be able to do this).
Lucky for you, your Marantz has pre-outs (and channel gain control), so it would work as a pre-amp for you. You probably could start with a 555 on the woofers and just the Marantz's main outputs for the mids/highs - it will be stable into the Ren 90's 4 ohm load, and will provide enough power for all but the loudest volumes. Typical power loads for the Ren 90's mids/highs in a medium sized room at low to moderately high volumes are more like 0.1-10 W/ch - but to avoid frying the planar drivers with clipping no matter how loud you play, it's definitely advisable to run something more powerful (or a tube amp that soft clips). On the other hand, the tweeters do have a protection circuit that will cut power to them if they're overloaded. The mids don't, however.
Now, Infinitys were always tuned to/with tube amps - Audio Research ones in particular - as the ideal amplifiers for the mids/highs. I've never heard Infinitys through one but I'd certainly like to try - the high output impedance of tube amps will certainly have an audible effect on the frequency response of the speakers.
Granted, I don't know if you'd even consider using your receiver as a pre-amp and the mids/highs amp. I would myself, at least as interim measure, considering how amazingly well mid-to-high end receivers perform. If you don't, and you run the speakers biamped, remember that you'll need a preamp with two volume-controlled outputs (I use a Carver C-11). At the very least, I'd use it as a pre-amp with (a) separate power amp(s) myself.
If you did, you'd have enough money to get a McIntosh MC2255 or MC2205 if you wanted - or a cheaper, less powerful Mac like an MC2100 and a 555 for the woofers. Actually, the MC2100 is probably tops on my list of relatively affordable amps to upgrade from the Carver.
As for running your music from your computer - if your computer is a dedicated media PC in the same room as your stereo, you would have no reason not to run an S/PDIF connection from the computer to your receiver. If you're running HDMI to the receiver from the computer, that would work perfect.
If it's in another room - there's lots of streaming products out there. I'd get a Logitech Squeezebox Touch myself - it has bit-perfect output, S/PDIF output, FLAC support, and up to 24 bit 96 kHz audio support (which I don't think makes any difference, but others do...). That's a heck of a lot for $250!
If you didn't want to run from the Squeezebox's analog output or (preferentially) use the S/PDIF input on your receiver (which I would definitely recommend - there's little to nothing to be gained by upgrading your DAC beyond that despite what subjectivists and pseudo-objectivists may claim) - then pro audio interfaces almost exclusively provide the best performance per dollar. In particular the Behringer SRC2496 and Creative E-Mu 0404 are among the best short of a Benchmark DAC-1. Again, I'd just stick with the DAC in your Marantz.
Also, to any other Renaissance 90 owners out there:
What, if any, difference is there in sound with/without the grilles? Is the difference mostly a with/without the fabric thing (perhaps a veil or slightly subdued treble with the grilles on), or does the shape of the grilles really make an audible difference as far as diffraction (imaging should be better with them on)?
Mine are broken and I'm not sure if it's really worth building replacements for them now - I may just keep an eye open for someone parting a Ren 90 out instead.
