I would agree with most of what Treitz3 has to say on this matter. The sonic signatures of the Carver M-4.0t and the Sunfire Symphonic Reference amps are VERY different.
In fact, the sonic signature of the Sumfire Symphonic Ref is also VERY different from the "regular" Sunfire stereo amps, and many would say that it is slightly inferior, ESPECIALLY when driving a difficult load like MLs.
You say you have Aerius I and Sequel II speakers. I am a long-time Carver owner as well as owning a set of ML Sequels (the original ones), and I can tell you that the M-4.0t will sound VERY sweet with your Sequels, and probably just as good with your Aerius. It will, however, be a little soft in the bass department. If you listen to a lot of acoustic music, or jazz, the M-4.0t might be just fine, but if you like lots of bass-heavy rock-n-roll, or BIG orchestral music, you might find it a little lacking in the "umph" department...
As Cherian says, the Carver amps have been out of production for about 15 years. However, they are perhaps the ONLY amps from their era that are still in VERY common use, and tend to hold up pretty well. And there is an active and knowledgeable user base, and at least two or three VERY reputable repair shops that can get your Carver gear fixed up to better-than-new if you have problems with it, for just a few hundred dollars per unit. In the "high end" world, the only other brand of amps that has similar long-term reliability, and is as well-supported by users and qualified technicians is perhaps McIntosh or Bryston. Just try getting your 1980's era Krells or Levinsons re-capped--you could buy brand new amps for less, I'd wager...
One caveat about Carver stereo amps and ML speakers though--you pretty much can forget the idea of getting TWO M-4.0t's and running them bridged mono. Carver amps will DEFINITELY crank when bridged mono into an 8-ohm speaker, but your Sequel II's are going to suck the juice right out of mono-bridged Carver stereo amps LONG before you reach "loud" levels. I've tried several Carvers this way with my Sequels (M-500t's, M-200t's, M-400t's, TFM-35's) and the wheels just fall off at medium-high volume levels--the bass gets all floppy (due to the damping factor of the amp being halved by bridging) and the mids get very grainy (due, I believe, to the amps rails being a little strained by the low resistance load of the speakers).
The Sunfire Symphonic Ref is sort of Sunfire's "budget" line. It's not really meant to drive difficult loads with the ease and grace that the 300x2 or 600x2 Signature amps can, and probably doesn't sound as smooth and authoritative as the new TGA two-channel models either. It will probably give you tighter bass than the M-4.0t though, but at a little sacrifice in sweetness on top and liquidity in the mids. Also, be aware that Sunfire's Symphonic Reference amps are the ONLY stereo amps that Sunfire made that simply CANNOT be bridged mono. The design does not allow for this at all.
The Sunfire 300x2 or 600x2, however, CAN be run bridged mono, and will do so into ML speakers with a LOT less trouble (and a LOT more authority and finesse) than Carver amps bridged mono. Gotta love that ultra-high-current topology and the astounding wizardry of Sunfire's power supply...
If you're going to get a used Sunfire, I'd suggest tracking down a 300x2 or 600x2. You'll be much happier, I think. The Sequel line is notoriously power-hungry, and will only sound better if you're feeding it with an outrageously high-current amp. I run a pair of Carver Silver 7t monoblocks on my Sequels, and they sound delightful. And all the headroom that the S7t's provide really does wonders for the bass deficiencies of the Sequels. They sound a LOT more authoratative with the Silver 7t's than any other amp I've had them hooked up to in the same price range (small Krells, Brystons, Adcoms, Rotels, smaller Carvers, etc)
One of the reasons that Plinius, Krell, Levinson, and ARC amps sound so good with ML's is because of their high-current outputs. It's not all about watts, bro--with ML's it's more about the CURRENT your amp can push, and the amount of headroom it has when driving a low-ohm load.
Oh, and you need to look into some REALLY fast speaker cables too. Properly matched cables can mean the difference between "OK" and "WOW" when it comes to Carver/Sunfire and ML speaker combos. I would HIGHLY recommend that you look into some used Nordosts--Solar Winds are pretty reasonably-priced on the used market, and you can often get the more upscale Red Dawns for less than 50% retail if you buy used. It has been my experience that Nordost speaker cables REALLY bring the speed of the MLs out when driven by Carver products.
But of course, YMMV...
--Richard
