Debating between Mcintosh SS or tube monos.

The 2301s provide a touch more sweetness and dimensionality to the presentation than SS. SS has a slightly tighter bottom end, but the 2301s certainly do not lack for bass. I must confess to being a tube fan who in my prior system chose Mac tubes over SS. A 4 year old well cared for pair of monodsis no issue as long as the tubes are not too old. Worse case, replace the tubes.

Tubes are kind of a pain to track down and buy. They generate a good bit of heat. You really have to be ready to commit. The 611s is not harsh at all. I have not heard the 2301s.

I heard the 611s with a tube 2700 preamp on a pair of 802D4s. To me the 802D4 is a bit of a harsh aggressive speaker but it seemed fine on that combo. Very detailed while a bit thin in the upper mids (speaker issue IMO).

I think McIntosh tube amps/pre are a little less “tuby” than some brands.

The MC2301 certainly does not lack bass…it’s the amplifier speaker combination which causes the perception that bass might be lacking. I used to drive B&W N800s with an MC2301 with great bass control and authority. The 800s were inefficient (89db) which caused me to turn the volume up to play decently. The bass was incredible though. The Mc2301s were very warm to the touch at constant 100 plus watt listening sessions. I now have field coil horn speakers, Classic audio Loudspeakers T1.5 reference which are way more efficient  (102db or so) and much much larger than the 800s..the bass is dynamic, deep, and articulate. The MC2301s run cooler now since I only need 30 watts to create a rock concert experience in my previous room, 30x20x8. Only occasionally did I crave extra bass if I waned to add club or rock concert feeling into my listening space. Otherwise, this combination is excellent. I have heard the MC501s, not the 611, but these are great products as well. If you do go tubes, then you must accept that tubes must be replaced every so often as they have a tendency to lose their luster and listening qualities as they are used over a period of time. This is of course dependent on type of tube and how long your listening sessions are. Using efficient speakers with a tube amps is an ideal combination. I believe generally speaking that If your speakers are not efficient ,you will not be happy with a tube amp. There is a lot more to inefficiency and driving speakers like this with tube amps. I know of two tube amps that drive speakers to room shaking bass with the speakers I mentioned, the MC2301 and Atmasphere NOVACRON. Of course there is a lot more to efficiency, but the pairing of speakers with whatever amp you decide on is crucial to obtain the best quality of music. 

1. inefficient speakers: tube preamp/ss amp. unknown future speakers: tube preamp/ss amp.

2. efficient speakers, tube/tube

I always recommend limiting speaker choices to efficient ones, the primary purpose is to be able to try/use tubes to start or eventually.

There is no way I would want a big powerful hot tube amp.

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Inefficent speakers: I used McIntosh SS C28 preamp with McIntosh SS MC2250 (250 wpc, tested by McIntosh accurate to 305 wpc).

Then I went back to my very efficient horn speakers, sold the SS set, and back to tube pre/tube amp.

over the years: 3 different tube setups: 30 wpc mono-blocks Fisher 80az; 35wpc receiver Fisher 500C; and now 45wpc Cayin A88T (wanted remote control).

Always Tube Preamp: McIntosh mx110z into whatever.

Don't let tube life be a big concern, they last quite a long time. 

I am like a broken record, repeating: if you get into tubes, get thee an inexpensive tube tester.

I have both. 601 model blocks and MC 275 take them out of blocks hands down over the tubes add higher volume levels and listening to the 601s have so much less distortion. I think that’s where they get that sweetness people talk about, but I only found that charming at lower levels. Hope that helps. You could always horizontal bi-amplify and you would get the best of both worlds.