Between the 2 I'd go with the Naka. Although actually both amps are underpowered for your sub. Looked around for some more options but din come up with anything at your current budget. Maybe the other guys will have more luck.

If there's nothing wrong with your current amp, why dun you use 1st and save up more $. If you backside itchy to buy something, your choice of HU might need some attention.

BTW, Zenn is selling the same Alpine amp for rm600 new.

The 2 amps give 180 and 200w (if i remember correctly) and your sub needs 250w. Which means ideal is a 300w amp. So yeah, the 2 amps are underpowered. you'll have bass, just not the best bass that the sub can give you. Will be more sluggish.

I reckon a HU change will improve your SQ more than an amp change, unless your present amp is a really really low end chicken.
Can get a P80RSii for around 1k used.

If you can explain exactly what kinda sound is missing from your system, will be easier to help you. eg. not enuf bass, fronts not clear enuf, everything not smooth or slow or no kick.

I drive a swift. I have:
1 4ch amp
1 monoblock
1 EQ
1 Xover
2 1F capacitor
10" sub
1 pair of custom passives in 2 boxes
A lot of other small stuff

Trust me, you can fit it in and still have 75% of your boot space. The mono can put underseat what.

The rubbish in rubbish out term is just general. Your Kenwood is not really that bad. Dun change also nvm. Just that a jump to a P80 for instance will result in very significant SQ gains. More than an amp change, I feel.