ProAc D25 or ProAc 1SC + Sub

What will be the best solution?

Theorical observations (guessing):

1SC + SUB will have deeper bass, better for home-cinema and some types of music. It will also integrate better in small rooms, since the sub usually has many controls.

D25 may demand a larger room but will have much better integration and a more balanced sound.

Which one is more holographic?
Which one is more dynamic?
Which one?
1st, you can't really go wrong with either selection, as long as you make a good choice for the Sub with the 1SC's. (I'd recommend a REL, or MJ Acoustics) Based on your 3 last questions, I'd go with the D25s. I've heard the D25s in a small room, 10x15 and they were fantastic. They have enough bass that no sub is required. And they will play louder and be more dynamic.

The 1SC's with a sub will give you more rumble, and would be my choice if space was an issue. They both have lots of magic, a "you are there" sound. The D25s will also allow you to keep improving your front end, where as the 1SC's will sound great in a more moderate system. But you'll hear a greater difference with the D25s as you pair them with better equipment.

I've heard them in an Ayre system before, (CX7 player, K-5 preamp, V-5 amp) and have yet to hear a better coherent, wide, deep soundstage and overrall musical cohesion and transparency. The D15s are an exceptional value also.

Good luck with your decision,

I personally would go for the Proac D25, which is a very good speaker in its class. Its brand new, has excellent frequency response, down ported, and uses excellent driver from volt, I dont even think you need a subwoofer if you opt for the d25s. Also Proac should be in the process of changing the response 1sc to a new model anytime soon, so it might be in your best interest to wait it out if you do indeed go for the 1sc. Match it with the er1 sub, they will make perfect compliments, also dont overlook the reference 8 signature in your decision making, it is also a very fine speakers.
Some very good points have been made above. And I competely agree that a lot will depend on the sub you pick to accompany the 1SCs.

I been switching off between Tablette 50 Signatures and Response 1SCs with an NHT sub for the last three years. But it wasn't until I bought a pair of Response 2.5s earlier this year that I realized how poor my sub was. Coherency and bass delineation with the 2.5s is far superior in my system than 1SCs and a sub. This could however be a completely different story if you use a sub like the REL or velodyne Digital Drives instead.

From what I understand, the D25 has better bass extension and presence than the 2.5, but I chose the 2.5 instead because of the lower price and I'd heard the they were faster sounding than the D25s. I still feel the 2.5s need a sub, but you might not feel that way with the D25s.

1SCs with a GOOD sub might fill the bill for you, plus it could also give you more adjustability and better tweaking options than the D25s. In my 12' x 16' room I think the 2.5s actually disappear better than the 1SCs or Tab 50 Sigs, and along with the better articulated bass, is what clinched it for me. Friz' point about the better upstream components paying a bigger dividend with the D25s than the 1SC is something I look forward to experiencing some day.

I think the best way to mate the 1SC with a sub is to run them full range and allow the sub to fill in the bottom octaves. Using a high pass filter ahead of the 1SC will kill the ProAc midrange and the "you are there" sound Friz mentioned. For this reason, I believe the D25s would definitely crank better than the 1SC with a sub because of their larger midrange/woofer. In a small room this may not be an issue, but it is something to consider.

I'd been spending so much time finding the right components, cables and tubes to produce the midrange I was searching for with my 1SCs that I'd neglected detailed and realistic bass. The 2.5s have provided this for me, and for this reason I plan to sell my 1SCs.

Good luck!
Thank you all for you kind advises!

The close replacement of the 1SC is an important argument to take in consideration. It is a quite dated model.

From your experience, do you believe the D25 needs some space to expand the bass or is it compatible with small rooms?
The response d25 should be compatible with small rooms. I am actually using a d15 in a 11*13( give ortake a few inches) bedroom system, and it has enough soundstaging and dynamics which nearly match my reference proacs in my larger room, wich is only 12 ft wide. I was actually thinking aof getting a d25 for my bedroom, but the price difference made it better for the d15, but the downporting and size should make it compatible for a smaller room.
I agree, the D25's imaging and depth work great in a small room. You only have to sit 6-8 feet away from them to enjoy the soundstage they present. They are 1 of the few speakers I've heard that sound great in both small & large rooms. If your room size doubled in a few years, they still have the ability to fill it with plenty of bass & still sound great.

Also, if you were going to go with monitors, I would look at the Ref. 8 Sig's instead of the 1SC's. They are $1200 new, and a better value in my opinion. I think with your bass considerations the D25's make more sense, but you could match up a pair of Ref. 8 Sig's with a REL Storm sub for about 1/2 the price. And there's always the D15's in the middle performance\cost wise. You will be happy with whatever you decide, but the D25's are the easiest solution with the most upside.
I have not had a chance to try D25's. But have owned 2.5's and 1SC's. I sold my 1SC's to purchase 2.5's in the search for deeper bass and was sad to find that most of what I loved about the 1SC's was not there with the 2.5's. I would strongly suggest that you audition both in your home for as long as you can. I am currently searching for a Sub that will work with 1SC's, as I have returned to them. I find with my gear the 1sc is superior in every way other than they lack deep bass. The 2.5 would probably like more power (assumed) than my cj premier 11A provided, although it drove them fine. I am sure that ProAc will change the 1SC sometime in the future. Not too sure about soon, as stated above. It is the only speaker in the line that has not been upgraded or changed in the recent past. The 2.5 and 3.8 are both newer models than the 1sc as well as the 1.5 being newer.... They have all been replaced by the D15 D25 and D38.... What do you think the reason for that is? It could be a lot of things!