I disagree with the advice given you so far.
It distresses me when I see advice given to ditch a really nice legacy system. With your budget you can not come close to what you have now, especially those speakers.
You can easily use all you have now except your NAD preamp.
All you need a a good low powered receiver and a sealed sub like one form SVS. This will be within your budget and you will have a far better system than most members on this forum
First of all your speakers are excellent. A center speaker is not only not necessary, but should not be used with electrostatic speakers like that. As Quad point out you won't integrate the center and electrostatics will give you a very stable center image.
It is far better to have two good speakers than five or seven lousy ones. That is the way you are heading.
So get one or other of these receivers and replace your preamp with it. Both of these have 2.1 preouts, so you can connect to your Carver amp and drive a sub.
Now all you need is a good sealed sub. It will not need to be powerful as it will just be supplementing those panels.
When you set it up set the panels to large and set it to LFE + main and set the crossover to the sub at 60 or 80 Hz and set the level to taste.
You can add surrounds now or later if you want and the receiver will power them.
Now you will have salvaged and updated a nice legacy system, that would cost you a fortune to replace if you pretty much start from scratch.
Thank you TLS Guy. I did not understand previous posts to include any part of my existing system. Sorry I missed that Markw.
I thought previous posts were proposing 2 separate systems, one HT one keep the audio I have for what it is.
TLS Guy, I do have a fantastic centre stage sound field. That's one thing that many enthusiasts dislike about speakers than have a "sweet spot"
and these indeed have that. If I'm listening to music and fall asleep, when someone walks in front of a speaker, it wakes me up
as the sound field collapses. I have them out from the wall 3-4' so the sound does indeed wrap around and provide an invisible sound point
meaning, when set up properly and acoustics are fairly optimal, (mine are not where I live now) the speakers disappear and voices and instruments
audibly appear to come from different elevations and distances. Many do not understand the panels force sound out the back as they do out the front.
Now what I am very very confused about is the NR1504 and using my amp. I am stumped.
Quoting the Marantz page you so kindly linked...
High power 5 channels amplifier with discrete output devices
Featuring identical circuit topology over all five power amplifier channels that are each rated at 60 watts,
the NR1504 is equipped with discrete high current output devices. Since all five amp channels are of the same exact design,
there’s no variation in sound quality between channels at all, for a true high fidelity surround sound listening experience.
You said using a low power amp, so I am confused, sorry.
Also, @60W/ch X 5 (I'm not aware yet of the said 2.1 and how that will work with the amp)
is not enough to drive my speakers and could damage them as I'm sure you picked up on
the post where I said they require 100W/ch @ 4 Ohm. I do not mean to insult your intelligence
by pointing this out, but my ignorance is not so blissful ATM
Also, the amp, requiring a passive input from the current pre-amp,
as I understand it, no power can be applied to the input of the amplifier,
so forgive me for asking, but how do I go about protecting my Carver?
I would like to say at this point, my Carver TFM-45 is supposed to be sonically
"cloned" or tactfully replicating, in solid state, what the amps in my Avatar are (Silver Sevens), in their tube style.
So if indeed there is any way I could incorporate the most of my sound system into a 4.1 that would be splendid!!!
Now for the crossover(s)
1 sub or 2? One is all the bass my wife would care for, and volume wise would be perfect for the level
of sound we ever play movies at. Would I just flip the cross over on the back of both of my speaker drivers
to the PASSIVE sub woofer via a pair of monster cables plugged into a wye or 3 way splitter, into a single sub?
See, if I use the crossover on my speakers, the sub has to be non powered. None of which have been recommended yet,
so really I thought we were looking at 2 totally different sound systems.
I do like the slim line effect the Marantz has, but see issues using my current amp with it given my old school status.