Bryston 4BSST or 6BST or 7BST

I am looking at various Bryston amplifiers for my system. On the used market I can get a 4BSST for around $2200, a 6BST for around $2900 and a pair of 7BSTs for around $2900. Which amp is better sounding and which is the better deal? I will likely upgrade a few years down the road so I am looking at resale value as well.

Any difference in sound quality between 6BST vs 6BSST?

I appreciate any comments.
The SST series amps have a more refined top end, and therefore are in more demand. I'd go for the 4B SST based on that alone, notwithstanding it's better sonics.
As an owner of Bryston 4B-ST and 5B-ST amps, and someone who has also done fairly extensive listening to the newer SST models, I have concluded that the SST models have somewhat different sonic characteristics than the ST models, but I'm not sure I'd go so far as to say they are "better". Some owners of Bryston amps, as well as several audio reviewers, have said that they prefer some characteristics of the ST line to the SST line, but it would take very good speakers and a discriminating ear to hear much difference between the ST and SST models.

The 6B-ST is a 3-channel amp that has the same power rating in each channel as the 4B-ST (it actually uses 3 of the same amplifier modules as found in the 4B-ST).

Unless you really need a LOT of power, in which case the 7B-ST monoblocks are a great choice (and an excellent buy at $2900), I'd probably opt for the 4B-SST and save some money for later upgrades. The 4B-SST is an excellent amp, and is rated very conservatively at 300 wpc (actual bench tests reveal that it could be rated at about 350 wpc).
If you need the power, then the 7BST is the way to go. I had it before I moved on to the Pass X-600. It was an excellent musical (as well as powerful) amp for my B&W Matrix 802s even if it lacked the ultimate in tonal refinement that the Pass provides in spades. I believe the Bryston products, because of their incredibly generous warranty of 20 years and workmanship, do keep their resale value well. I found that to be the case when I sold mine.

(I listen to mostly classical music, if that is relevant information for you.)

Best regards.
From what I have heard between the 4BST and 7BST, the 7BST was better sounding in terms of dynamic and drove the speakers with ease. More open and relax sound than the 4BST in the Joseph Audio RM-22 and RM-50 speakers. If I'm going with Bryston again then I would definitely consider 7BST over 4BST
Vvrinc, how did you compare the bass (200hz lower) between 7BST and X-600 ? Transient ? I want to use it as bi-amp.

The Bryston lacked only the subtlety of the Pass. The Pass is just more refined from top to bottom. However, in bass-slam, decay, the Bryston held its own very, very well. I had originally replaced the 7BST with the 7BSST only to discover that I liked the sound of the older model better. I sold the BSST and kept the BST until the move to Pass.
(Please note that I also prefer the sound of the Matrix Series III line of B&W to the newer Nautilus so if the words “old fart” come to mind as you read this post, it would be understandable.)
If you have an opportunity to hear the Bryston, I would recommend it.
Vvrinc, thanks for your comments. I find that interesting that you prefer the sound of the 7BST to the newer 7BSST. That is one reason I would steer away from the 7BST and get the 4BSST - because I would assume that the SST would sound better. Are the differences between the STs and the SSTs that pronounced that it is worth the extra money. I am still undecided which amp(s) to buy as there does not appear to be a clear winner except that nobody has really said much about the 6B.
I owned both the 4B SST and 14B SST. I purchased the 14B SST over the
7B SST monos due to space considerations, slightly less power
consumption and heat production. The 14B SST had better bass control,
had better low level detail and played more dynamically at lower
volumes than the 4B SST. If I had to do again, I'd purchase the 14B SST.
I compared the 4BST and the 4BSST and ended up purchasing the 4BSST because of the refinement in the top end. It simply sounded more natural to me
I personally preferred the SST series over the ST. Like others here I prefer the added smoothness and refinement and found them more neutral and less bright. But there are people who preferred the "hotter" balance of the ST series and found them to be more dynamic and involving.

I think the best thing to do is to compare an ST amp with their subsequent SST replacement. But of the amps you mentioned, there's no question to me that the 7BST will be the best amp. First of all, you won't find too many people who actually think the SST series to be a quantum leap in advancement. And second of all, the 7B will be much more dynamic and throw a much deeper and wider soundstage than both the 4B and the 6B regardless of whether it's ST or SST. The 7B is simply a better amp.
I would definitely agree with everybody who has posted that the SST series is better than the ST series. I have owned all 3 versions of the Bryston 3B - 3B, 3BST and 3BSST. Each one is incrementally better than the previous version but none is a huge improvment over the previous one.

Ultimately, I am looking for the best sound. I think the decision is fairly clear for me - the 7BST is the better choice over the 4BSST or the 6BSST.

Thanks to all who replied and helped me out here.

I have had both the 4B-ST and the 4B-SST in the same system and preferred the SST. It was smoother on highs and middle and retained the solid bottom end Bryston is known for.

I could be wrong but I think as far as the 6B's go the ST is nearly identical to the SST. It was designed just before the new names and corresponding faceplates. Though it would be better to check with Bryston directly.

You will get better separation with the monos and clearly more power. Though I digress, depending on your taste and associated equipment your mileage may very with each unit listed. Personally the 4B-SST was enough.....for now.
I have had experience with the Bryston 7BST on my B&W Matrix 800's in my second system and have tried them on my JMLab Utopias, which used to have Pass X600's. The 7BST's are an excellent match to any speaker that needs a lot of current to control and drive the bass, which any of the large B&W series really needs to keep them from getting "muddy". Overall, having to chose between the Pass X600's and the Bryston 7BST, I would keep the 7BST. They give up very, very little to the Pass X600's in the highs, nothing in the mid and kill the X600's in the bass and overall response. I am switching to Wilson Benesch Chimera's and will probably use the 7BST's on them, unless I switch to tubes. I agree with the comments that the difference between the 7BST and 7BSST is hardly perceptible.
I would also comment for guys getting into B&W to buy the older Matrix series as they are better speakers then the Nautilus series. Since B&W got bought out, they have gone to more mass market, then to keeping their previous quality and sound. A pair of Matrix 800's or 801 series 3 is a much cleaner speaker (in the B&W series) then anything they have new. Look at all the Nautilus series that are for sale and notice that the price on the Nautilus 801's are dropping, there is a reason. Good luck
I recently had the experience of directly comparing the 4B SST to a pair of 7B SST driving the same speakers from the same source. I can say that the improvement over the 4B SSTs was so noticeable and dramatic, that I am getting the 7B SSTs.