AGI 511A driving either a Forte' 3, 4/4A or a 6/6A ( depending on power requirements ). If you shop carefully, this combo should be available for about $6-650 or so.
The AGI is a phenomenally fast preamp that makes other preamps sound slow and veiled. In stock form, it is capable of very good performance when properly set up. It also happens to have a very good phono section in it, one which rivals those costing hundreds if not thousands of dollars. This preamp can be modified for world class performance due to forward thinking of the engineer and the very short yet excellent circuit he came up with. Obviously, one can "go to town" and spend a lot using premium parts or perform some very simple yet basic upgrades that are quite effective sonically and monetarily. Due to their age though, it is possible that any AGI's purchased on the used market may need a small amount of TLC. Keep this in mind for any / all used components that have been around for a few years or more.
One word of caution about the AGI. Since this is a two pronged power cord without being polarized ( both prongs are the same size ), one really has to check for proper plug orientation for best results. I have mentioned this to a few others running this preamp and they have told me that they can't believe the difference that this makes on this component. Then again, when something is designed for optimum performance, changing ANY of the variables is bound to result in a noticeable shift in the parameters of operation. Most gear isn't designed this well, so the differences in AC polarity aren't as obvious.
As to the Forte's, these are the "budget" amps that Threshold offered. The model 3 was built and designed by Nelson Pass and is a bi-polar design. It is VERY "sweet & airy" but slightly lean sounding in most applications. It is rated at 200 / 350 wpc. Nelson Pass sold Threshold / Forte' to PS Audio and the amps after the 3 were built and designed by them. Quite honestly, these amps are better than anything PS has ever offered to date by a wide margin. The 4/4A is a Class A amp rated at 50 / 80 and sounds very good with better tonal balance than the 3 but possibly not quite as "airy" or "delicate" sounding. The 6/6A is the Class AB version of the 4 and is rated at 200/350. It offers more headroom than the 4 ( obviously ) and can be a little "bloomy" or "full bodied" sounding. Depending on your power requirements and the tonal balance of your speakers, one of these is bound to work. The difference between the 4/6 and the 4A/6A is that the "A" versions offer balanced ( XLR ) inputs.
The one drawback to the 4's & 6's are that they use specific output devices that are no longer manufactured. With that in mind, a good tech could subsitute other parts ( for both channels in entirety ) and still keep the amp running with nary a problem. The parts for the 3 are still available, so that should not be a concern if looking at one of these amps.
All of this gear sounds markedly better if left on 24/7. Since all of these amps are of a high bias design, they DO run hot. If running a highly capacitive speaker cable or reactive speaker loads, i do recommend the use of a zobel network at the speakers. This will keep the amps from going into oscillation, resulting in more consistent sonics and performance regardless of the load. The preamp itself can't be turned off when plugged in even though there is a power switch on the front. All this switch does is to activate the switched outlets on the back of it. Don't use those outlets and leave the switch turned off.
Obviously, careful selection of cabling is required if you want to obtain the full potential of any system. Good cabling can be found quite reasonably if you play the "Audiogon game" on a regular basis. Using a system of this calibre WILL easily reveal the differences in cabling. As such, don't fool yourself into thinking that generic crap will give you the same results as more advanced cabling that takes advantage of higher grade conductors and dielectrics arranged in a more technically advanced geometry. A good pair of interconnects and speaker cables of reasonable length shouldn't set you back more than about $150-250 for a system like this. Lesser systems than something comprised of these components may be able to get away with lower grade signal cabling due to being less musical and revealing at the same time.
While i do believe that power cords can make a difference in a system, the AGI and the Forte' 3 both have captive cords while the 4 & 6 have IEC's. Either way, at this stage of the game and budgetary conditions, i would save power cord considerations for last after your initial investments have been secured and you are familiar with the potential of the components as they are delivered.
Please bare in mind that these suggestions are not to imply that there aren't other valid combo's out there. I'm simply trying to pass on some combo's that i know work well and offer phenomenal bang for the buck when properly set up. I haven't tried everything under the Sun, but i have tried these. I know that they work well together when mated as pairs to make up the back-bone of a very good but reasonably priced system that strives to offer "musical accuracy". Sean