It’s not that the JBL 1400 is a "horn loaded speaker" that is causing you to think you may need something warmer to tame it. It is because the 1400 has a titanium dome tweeter as well as an aluminum dome midrange driver. The breakup of metal dome drivers will cause a bright edge to the sound and this can make you think you need something warmer. It’s entirely possible, but also keep in mind that the 7Bsst2 amps are very dry and forward - these can definitely sound somewhat harsh with metal dome tweeters. It could give you a very hard edge type of sound.
Another thing to watch out for is amps/preamps that are very warm will, essentially, smear the high frequencies somewhat. This can also come across as harsh sounding, especially on metal dome tweeters. The Marantz 8802 is definitely very warm and will lose resolution or cause smear in the high frequencies. So, you already have two counts towards a harsher sound.
I would say to get the smoothest amplifier you think you can get. If that turns out to be a Parasound JC1, then fine. It could also be the Bryston 7b3 will be very smooth with its revised Class A input stage (the amp is still Class AB).
Another amp to consider at this point is the Krell Solo 375 or 575 monoblocks (575 is a lot more expensive - but I doubt that you will need more than 375 watts). The new Krell Solo and Duo amps using a sliding Class A bias that will give you the sound of bipolar Class A without the heat. The result is a very smooth sound. It has an ethereal and creamy quality to the midrange and will likely give you more resolution than the JC1s (the JC1s are based on a FET input stage which is not as clean or high resolution). Krell uses all bipolar audio stages. This new series is probably very much like the old Krell FPB series without the massive Class A heat. I think this will be a lot more forgiving on the JBL titanium dome tweeters and will not have the hard edge that many other amps will do.
The sonic signature of Class A differs based on design. The Krell bipolar circuit "Class A" sound is very smooth and creamy and ethereal, with clean clear high frequencies. The Parasound / Pass Labs "Class A" type sound is more warm / thick with textured thick mids and could have softer rolled off high frequencies. It is entirely a matter of taste and desired result here.
Finally, I would be careful of interconnect / speaker wire / power cord selection. With titanium dome tweeters, I would remove any silver or silver-plated elements in your system. Silver will push the upper mids/highs and make those titanium tweeters extra bright. It can also cause the midrange to be pushed into the artificial signature.
