We sold both Mac and Marantz back in the 70's and 80,s. The bass will be tighter with the Marantz amps and seem more extended and the highs will have an extra sparkle. Depending on the Altecs and which diaphragms are in the HF driver that characteristic can be a positive or real turn off. If you are after a more tube like sound you will prefer the Mac stuff for sure. The 2105 with an autoformers has a much lower damping factor making the woofers express them selves more like a tube amp would in the important midrange frequencies below 800 HZ or so down to 120 hz in my case. Some people call it tube bloom. And yes you can have similar sound from a 2105, 2100, 2505, 250 and 2300. I have a 2505 and it works beautifully with my remote Boston in wall room speakers. It Does well driving some of my head phones, too. In wall speakers tend to be a bit dry, but the 2505 as would a 2105 makes them sound very pleasing and enjoyable.
There are a few things you need to be aware of. Set the volume controls on the MAc amp at 12:00 oclock to get the best signal to noise distortion figures. With the Altecs you might set the controls down to 11:00 if you sit close to the speakers. Keep the speaker lines as short as possible and use 12 AWG wire. Not for the power but to get the best best performance. Early 2105's the meter switch was backward increasing the sensitivity on the way to the off position. And full power was indicated at 0 db. The later units the sensitivity started at the most counter clockwise position and then decreased on the way to the off position which kept the meters needles from being damaged. The 0 position on the meter was changed to 50 watts making +3 db the 100 watt indicator. That was to help prevent folks from over driving the amplifier. And remember a 2105 in like new condition puts out close to 140 watts before clipping. Never push either the Marantz or Mcintosh amp as they don't have protection and can easily damage your HF diaphragms. Especially if the speakers uses a 500 or 800 HZ crossover. 1200 HZ crossover effectively doubles the RMS power handling of the HF diaphragm. Preventing the aluminum suspension surround from fatiguing and failing. If the crossover is a 500 HZ type keep the level control as low as you can accept for the balance you want to prevent to much power getting to the diaphragm. A percussion cap made for later Altecs will help proect the diaphragm, too. If you don't have them see if they are available from Great Plains Audio in Oklahoma city.
I checked the specs and the speakers is rated at 50 watts RMS with an 800 Hz crossover. So you definitely don't want the meters on your 2105 to go above the 0 db indication. For the blink of an eye might be acceptable, but if you can think about the time, it's much to long. And as I remember the 416 woofer at that time was rated at only 75 watts RMS, So even just pushing the bass can be an issue with either the Marantz and Mcintosh amp.
Now the speakers are rated at 97 db 1 watt 4 ft, not 1 meter. So with 50 watts for each speaker thats 117 db and thats a lot of sound and way above concert level listening at 10 to 12 ft using both speakers. You are at Klipschorn levels so watch out and save your ears. A friend of mine had those speakers using a little 30 watt Mcintosh MA 230 integrated amp and that was plenty for he and me. I had Altec Carmels that used two 12 inch 414 16 A woofers instead and a MA 230 with 30 watts was plenty for me, too. I chose the 2 12's as they could handle more bass energy and in a larger enclosure reached lower in bass response and performed better above 400 HZ.
But if set up properly the 846 will perform very well. But be prepared to have to move them around a bit to get the most uniform response. If the bass is to boomy either elevate them so the horn is at ear height or pull them out from the wall and tip the speaker up facing you directly. When finished you should get some of the best vocal sounds you have ever experienced.
